Michigan licenses CPAs and CPA firms through the Department of Licensing and Regulatory Affairs (LARA) under the Occupational Code; a firm using the CPA designation needs a firm license, which a non-CPA buyer cannot hold. Tax preparation and bookkeeping are unlicensed at the state level; preparers need an IRS PTIN. The Occupational Code keeps information from a CPA's professional services confidential without the client's written permission, and we found no Michigan rule specific to the sale of a practice.
For AICPA members, interpretation 1.400.205 applies: a written consent request to each client, consent presumed after at least 90 days, and no file transfer before then. Tax return information may be reviewed by a prospective buyer under a written confidentiality agreement (Treas. Reg. §301.7216-2(n)). The Michigan Association of CPAs publishes broker-written guidance on how practices are sold; entity records are on LARA's business entity search.
Sources: Michigan LARA, Accountancy · AICPA Code, ET §1.400.205 (PDF) · 26 CFR 301.7216-2