Honestly, being an SP myself I don't expect tips from the guys that come and see me. I work with ASA, so I don't get the full amount that the client gives me, I split it with the agency. However I do get more than %50 of the money, and its all cash. Tips are nice, but far from necessary.
My favorite 'tip' was not in cash, but in the form of a gift. I greeted a client at the door and they had brought me a carnation. I found that to be a very sweet gesture, especially since I love carnations. That is much preferable to a cash tip in my opinion.
james t kirk;

there are girls charging $250/hour? And then expecting tips? Shit, my agency is under-charging xD