Many of the male clients at SW5 - a much missed project for male and trans sex workers - used to leave getting the money until afterwards in the hope of ending up with more via a tip.
I was astonished at this. As well as ignoring the basic rule, they were men seeing other men and must have known from personal experience that what seems a good idea when you're horny does not always seem like a good idea after you've come. But male 'I can look after myself' plus greed makes for risk taking...
Every so often, one of them would get burnt as the punter went 'You know what, maybe paying for that sex wasn't such a good idea' to themselves. They'd complain about it to us and we'd have to tell them that there was nothing they could do about it. Did that ever stop them doing it? Ha.