Ex. 5.8(a)-1 EXHIBIT 5.8(a) To the Agreement and Plan of Reorganization FORM OF SMMF AFFILIATE AGREEMENT THIS AFFILIATE AGREEMENT (the “Agreement”), dated as of August 24, 2023, is by and among BURKE & HERBERT FINANCIAL SERVICES CORP., a Virginia corporation (“BHRB”), SUMMIT FINANCIAL GROUP, INC., a West Virginia corporation (“SMMF”), and the undersigned shareholder of SMMF (“Shareholder”). All capitalized terms used herein and not defined herein shall have the meanings assigned thereto in the Merger Agreement (as defined herein). WHEREAS, the Boards of Directors of BHRB and SMMF have approved a business combination of their companies through the merger (the “Merger”) of SMMF with and into BHRB pursuant to the terms and conditions of an Agreement and Plan of Reorganization, dated as of August 24, 2023, by and between BHRB and SMMF, and a related Plan of Merger, a form of which is attached as an exhibit thereto (together, the “Merger Agreement”); WHEREAS, Shareholder is the beneficial and/or registered owner of, and has the sole right and power to vote or direct the disposition of the number of shares of common stock, par value $2.50 per share, of SMMF (“SMMF Common Stock”) set forth below Shareholder’s name on the signature page hereto (such shares, together with all shares of SMMF Common Stock subsequently acquired by Shareholder during the term of this Agreement and over which such Shareholder has the sole right and power to vote or direct the disposition, but excluding the shares of common stock described in the last sentence of Section 5(a) hereof, are referred to herein as the “Shares”); and WHEREAS, as a condition and inducement to BHRB and SMMF entering into the Merger Agreement, Shareholder has agreed to enter into and perform this Agreement. NOW, THEREFORE, in consideration of the covenants, representations, warranties and agreements set forth herein and in the Merger Agreement, and other good and valuable consideration (including the merger consideration set forth in ARTICLE 2 of the Merger Agreement), the receipt and sufficiency of which are acknowledged, the parties hereto, intending to be legally bound hereby, agree as follows: 1. Agreement to Vote. During the term of this Agreement and at such time as SMMF conducts the SMMF Shareholders Meeting, except as provided in Section 5(b) hereof, Shareholder agrees to vote or cause to be voted all of the Shares, and to cause any holder of record of the Shares to vote all such Shares, in person or by proxy: (i) in favor of the Merger Agreement at the SMMF Shareholders Meeting; and (ii) against (A) any Acquisition Proposal, (B) any action, proposal, transaction or agreement which could reasonably be expected to result in a breach of any covenant, representation or warranty or any other obligation or agreement of SMMF under the Merger Agreement or of Shareholder under this Agreement and (C) any action, proposal, transaction or agreement that could reasonably be expected to impede, interfere with, delay, discourage, adversely affect or inhibit the timely

Ex. 5.8(a)-2 consummation of the Merger or the fulfillment of conditions of BHRB or SMMF under the Merger Agreement. 2. Covenants of Shareholder. Shareholder covenants and agrees as follows: (a) Ownership. Shareholder is the beneficial and/or registered owner of the Shares as set forth below Shareholder’s name on the signature page hereto. Except for (i) the Shares, (ii) shares of SMMF Common Stock subject to outstanding SMMF RSU Awards and SMMF SARs (which shares, if any, are set forth on the signature page hereto), Shareholder is not the beneficial or registered owner of any other shares of SMMF Common Stock or rights to acquire shares of SMMF Common Stock and for which Shareholder has the sole right and power to vote and/or dispose. For purposes of this Agreement, the term “beneficial ownership” shall be interpreted in accordance with Rule 13d-3 under the Securities Exchange Act of 1934, as amended. (b) Restrictions on Transfer and Dispositions. Except as permitted by Section 2(e), during the term of this Agreement, Shareholder will not sell, pledge, hypothecate, grant a security interest in, transfer or otherwise dispose of or encumber any of the Shares and will not enter into any agreement, arrangement or understanding (other than a proxy for the purpose of voting the Shares in accordance with Section 1 hereof) which would during that term (i) restrict, (ii) establish a right of first refusal to, or (iii) otherwise relate to, the transfer or voting of the Shares. (c) Authority. Shareholder has full power, authority and legal capacity to enter into, execute and deliver this Agreement and to perform fully Shareholder’s obligations hereunder. This Agreement has been duly and validly executed and delivered by Shareholder and constitutes the legal, valid and binding obligation of Shareholder, enforceable against Shareholder in accordance with its terms. (d) No Breach. None of the execution and delivery of this Agreement nor the performance of Shareholder’s obligations contemplated hereby will result in a violation of, or a default under, or conflict with, any contract, loan and credit arrangements, Liens (as defined in Section 2(e) below), trust, commitment, agreement, understanding, arrangement or restriction of any kind to which Shareholder is a party or bound or to which the Shares are subject. (e) No Liens. The Shares and the certificates representing the Shares are now, and at all times during the term of this Agreement, will be, held by Shareholder, or by a nominee or custodian for the benefit of Shareholder, free and clear of all pledges, liens, security interests, claims, proxies, voting trusts or agreements, understandings or arrangements or any other encumbrances whatsoever (each, a “Lien”), except for (i) any Liens arising hereunder and (ii) Liens, if any, which have been disclosed to BHRB in an attachment to this Agreement. (f) Consents and Approvals. The execution and delivery of this Agreement by Shareholder does not, and the performance by Shareholder of his or her obligations under this Agreement and the consummation by him or her of the transactions contemplated hereby will not, require Shareholder to obtain any consent, approval, authorization or permit of, or to make any filing with or notification to, any Governmental Authority.

Ex. 5.8(a)-3 (g) Absence of Litigation. There is no suit, action, investigation or proceeding pending or, to the knowledge of Shareholder, threatened against or affecting Shareholder or any of his or her affiliates before or by any Governmental Authority that could reasonably be expected to materially impair the ability of Shareholder to perform his or her obligations hereunder or to consummate the transactions contemplated hereby. (h) No Solicitation. During the term of this Agreement, Shareholder shall not, nor shall he or she permit any investment banker, attorney or other adviser or representative of Shareholder to, directly or indirectly, (i) solicit, initiate or encourage the submission of any Acquisition Proposal, or (ii) participate in any discussions or negotiations regarding, or furnish to any person any information with respect to, or take any other action to facilitate any inquiries or the making of any proposal that constitutes, or may reasonably be expected to lead to, any Acquisition Proposal. (i) Statements. Shareholder shall not make any statement, written or oral, to the effect that he or she does not support the Merger or that other shareholders of SMMF should not support the Merger. 3. No Prior Proxies. Shareholder represents, warrants and covenants that any proxies or voting rights previously given in respect of the Shares are revocable, and that any such proxies or voting rights are hereby irrevocably revoked. 4. Certain Events. Shareholder agrees that this Agreement and the obligations hereunder shall attach to the Shares and shall be binding upon any person or entity to which legal or beneficial ownership of the Shares shall pass, whether by operation of law or otherwise, including Shareholder’s successors or assigns. In the event of any stock split, stock dividend, merger, exchange, reorganization, recapitalization or other change in the capital structure of SMMF affecting the Shares, the number of Shares subject to the terms of this Agreement shall be appropriately adjusted, and this Agreement and the obligations hereunder shall attach to any additional securities of SMMF issued to or acquired by Shareholder. 5. Capacity; Obligation to Vote. (a) Notwithstanding anything in this Agreement to the contrary, in the event that the Board of Directors of SMMF is permitted to engage in negotiations or discussions with any person who made an unsolicited bona fide written Acquisition Proposal in accordance with Section 5.5 of the Merger Agreement, Shareholder shall be permitted, at the request of the Board of Directors of SMMF, to respond to inquiries from, and discuss such Acquisition Proposal with, the Board of Directors of SMMF. With respect to the terms of this Agreement relating to the Shares, this Agreement relates solely to the capacity of Shareholder as a stockholder or other beneficial owner of the Shares and is not in any way intended to affect or prevent the exercise by Shareholder of his or her responsibilities as a director or officer of SMMF, including actions permitted to be taken in compliance with Section 5.5 of the Merger Agreement. The term “Shares” shall not include any securities beneficially owned by Shareholder as a trustee or fiduciary, and

Ex. 5.8(a)-4 this Agreement is not in any way intended to affect the exercise by Shareholder of his or her fiduciary responsibility in respect of any such securities. (b) The parties hereto agree that, notwithstanding the provisions contained in Section 1 hereof, Shareholder shall not be obligated to vote as required in Section 1 of this Agreement in the event that (i) BHRB is in material default with respect to any covenant, representation, warranty or agreement with respect to it contained in the Merger Agreement or (ii) SMMF is otherwise entitled to terminate the Merger Agreement. 6. Resignation of Director. In the event that Shareholder is not selected to serve as a member of the Board of Directors of the Continuing Corporation, Shareholder hereby agrees to resign as a director of SMMF and SCB, as applicable, and to deliver a letter of resignation to SMMF and SCB, in each case in the form reasonably requested by SMMF and effective as of the Effective Time. 7. Term; Termination. The term of this Agreement shall commence on the date hereof. This Agreement shall terminate upon the earlier of (i) the Effective Time of the Merger, or (ii) termination of the Merger Agreement in accordance with ARTICLE 7 of the Merger Agreement. Other than as provided for herein, following the termination of this Agreement, there shall be no further liabilities or obligations hereunder on the part of Shareholder, SMMF or BHRB, or their respective officers or directors, except that nothing in this Section 7 shall relieve any party hereto from any liability for breach of this Agreement before such termination. 8. [Intentionally omitted.] 9. Specific Performance. The parties hereto agree that irreparable damage would occur in the event that any of the provisions of this Agreement were not performed by the applicable party hereto in accordance with their specific terms or were otherwise breached. Each of the parties hereto shall be entitled to an injunction or injunctions to prevent breaches of this Agreement by the other and to enforce specifically the terms and provisions hereof in any court of the United States or any state having jurisdiction, this being in addition to any other remedy to which it is entitled at law or in equity. Each party hereto waives the posting of any bond or security in connection with any proceeding related thereto. 10. Banking Relationships. Notwithstanding any other terms and provisions of this Agreement, including Section 6, Shareholder further covenants and agrees that (i) from the date hereof and through the Subsidiary Merger Effective Time, he or she will use best efforts to maintain and continue with SCB such banking relationships (e.g., lending, deposit or other accounts, but excluding any relationships related to trust or wealth management accounts or services) (as applicable, “Banking Relationships”) that Shareholder (in his or her individual capacity) currently maintains with SMMF and SCB, in form and substance substantially the same as currently maintained, and (ii) after the Subsidiary

Ex. 5.8(a)-5 Merger and until the one (1) year anniversary of the Subsidiary Merger, he or she will use reasonable best efforts to maintain and continue with the Continuing Corporation and the Continuing Bank such Banking Relationships that Shareholder (in his or her individual capacity) maintained with SMMF and SCB prior to the Subsidiary Merger, but in each instance, for the avoidance of doubt, excluding any Banking Relationships maintained by Shareholder in a fiduciary or trustee capacity or any Banking Relationship of any entity that may be affiliated with such Shareholder. 11. Amendments. This Agreement may not be modified, amended, altered or supplemented except by execution and delivery of a written agreement by the parties hereto. 12. Governing Law. This Agreement shall in all respects be governed by and construed in accordance with the laws of the Commonwealth of Virginia without regard to the conflict of law principles thereof. 13. Notices. All notices, requests, claims, demands or other communications hereunder shall be in writing and shall be deemed given when delivered personally, upon receipt of a transmission confirmation if sent by facsimile or like transmission and on the next business day when sent by a reputable overnight courier service as follows: (i) with respect to BHRB or SMMF, the applicable address set forth in Section 8.5 of the Merger Agreement, and (ii) with respect to Shareholder, at the address for Shareholder shown on the records of SMMF. 14. Benefit of Agreement; Assignment. (a) This Agreement shall be binding upon and inure to the benefit of, and shall be enforceable by, the parties hereto and their respective personal representatives, successors and assigns, except that the parties hereto may not transfer or assign any of their respective rights or obligations hereunder without the prior written consent of the other parties. (b) The parties hereto agree and designate SCB as a third-party beneficiary of the terms set forth in Section 10 of this Agreement, with SCB having the right to enforce the terms thereof. 15. Counterparts. This Agreement may be executed in one or more counterparts, and by the different parties in separate counterparts, each of which shall be deemed to be an original, but all of which shall constitute one and the same agreement. A facsimile copy or electronic transmission of the signature page hereto shall be deemed to be an original signature page. 16. Severability. In the event that any provision of this Agreement shall be held invalid or unenforceable by any court of competent jurisdiction, such holding shall not invalidate or render unenforceable any

Ex. 5.8(a)-6 other provisions hereof. Any provision of this Agreement held invalid or unenforceable only in part or degree shall remain in full force and effect to the extent not held invalid or unenforceable. Further, the parties agree that a court of competent jurisdiction may reform any provision of this Agreement held invalid or unenforceable so as to reflect the intended agreement of the parties hereto. [signatures on following page]

Ex. 5.8(a)-7 IN WITNESS WHEREOF, BHRB, SMMF and Shareholder have caused this Agreement to be duly executed as of the date and year first above written. BURKE & HERBERT FINANCIAL SERVICES CORP. By: David P. Boyle Chairman and Chief Executive Officer SUMMIT FINANCIAL GROUP, INC. By: H. Charles Maddy, III Vice Chairman, President and Chief Executive Officer SHAREHOLDER [Insert Name] Number of Shares: Number of Shares Underlying SMMF SARs: Number of Shares Underlying SMMF RSU Awards: