A bit naive, perhaps, but I think it must be fairly common. A straight friend of mine, perfectly smart and whatnot, met some woman in a bar in Thailand and ended up spending his whole vacation with her. She showed him around and, um, I suppose other things too. No economic arrangement was ever explicitly negotiated.

After consulting a friend of his, he ended up "buying her off" at the end of the trip, for a rather generous chunk of change (hundreds of U.S.). A few weeks later, she emailed him asking for more money, with some sob story or other. Somewhat unpleasant, for him, I think.

It seems to me the best thing one can do in this kind of situation is to walk away with a clean conscience (be honest about your motivations, try to assess the counterparty's, and leave no-one too disappointed).