It's a fucked up request. If the escort knows he can't perform reliably for clients who are X, Y, or Z, then before finalizing the meeting he can ask the client "are you X,Y, or Z? I ask because, unfortunately, history has taught me that intimacy with men who are X,Y and Z, do not go well for me."
This avoids the fucked up practice of asking the client for photos, and minimizes the chances that the appointment won't go well.