Wealthier people can choose forms of exchange with more formalities and more ambiguity (and consequently more economic friction).
You've chosen good examples, but its often not that clear cut.
I have a friend who was once a (non-stripper) entertainer at a bar in Japan. Sex wasn't explicitly required, but boyfriends were forbidden, to make sure the customers felt they were in with a chance. Grey area. Not a big jump from there to some account management or acting careers.
And on the flip side, my neighbour had a favourite client she was always happy to see. And before I knew her, her last boyfriend had started out as a client.
I don't think its practical to distinguish, and I certainly don't think its practical to distinguish in a nondiscriminatory way.