This relies on the assumption prostitutes have no choice in what they do or do not do and who they do or do not take as clients to be an issue. In places where its legal or people doing it illegally by choice don't HAVE to do anyone or anything they do not want too; they can be as exclusive or as far ranging as they wish. And of course people doing it through choice are likely to be a bit more sexually adventurous than your average joe and enjoy trying out these "weird" things. Judging by the lifestyles of many of them, they don't make a lot of money, so they get whatever they can get. Say they have a choice between one client with a strange preposition and not getting one at all, they'd probably pick the former. People hiring prostitutes would probably be more likely to try something adventurous anyway because since it's illegal, it ends up being between them and the prostitute. Even if it was legal, it would probably be the same way (think of lawyer-client privilege and doctor-patient privilege). If you do something more adventurous (something that they would feel embarassed about because after all it's something personal) with a co-worker or girlfriend and someone found out (think of fights or break ups), it wouldn't be that great would it?