In what scenario is a commission prohibited for a CPA?

The scenario where a commission is prohibited for a CPA occurs when the client is a tax client and the CPA is providing attest services. This is due to the ethical standards set by the American Institute of Certified Public Accountants (AICPA) and state regulatory bodies, which emphasize the importance of maintaining independence and objectivity in performing attest engagements. When a CPA provides attest services, such as audits or reviews, any commission-based compensation related to the same engagement could compromise that independence, creating a conflict of interest.

In contrast, other scenarios may not inherently conflict with the ethical standards governing CPA conduct. For example, being unlicensed in a state simply means the CPA cannot legally practice there, and it does not directly address the issues of independence or ethical compensation structures. Similarly, it’s important for CPAs to disclose commission structures to clients, but the absence of full disclosure alone doesn't automatically prohibit commissions. Furthermore, if a client does not agree to a commission structure, that situation pertains more to negotiation and consent rather than an ethical prohibition against receiving a commission in general. Thus, the key focus is on the preservation of independence and objectivity in the context of attest services provided to tax clients, which makes option B the correct choice.