From comments around the forums, I gather that there is a mounting problem with clients attempting to pass fake banknotes off onto escorts.
While I deplore that completely, it occurs to me that it is only a matter of time before somebody works out that they can play the reverse game on clients. The client pays, the escort steps out of the room, switches the notes and returns to say that the money is fake. What can you do about this?
You could pay in small value bills - an escort trying this trick is unlikely to have a huge stack of faked fives and tens. You could even pay in coins - I bet that would get an odd look! :-)
A simpler idea is just to write down the serial numbers of the notes on a small piece of paper and then to check the numbers if this ever happens to you. Then you just say "This is not the note that I gave you. let's call the police and I bet that they will come and search this apartment and find a note with this number on it."
While I am sure that none of the escorts that I have met would do such a thing, I will be taking this precaution myself.
Also, I note that a number of profiles are offering to take credit cards. There is at least one factory in China that makes card readers with an extra little surprise inside. A cellular radio with a SIM card that sends card details (with PIN if used) by SMS to carding gangs. The carding gangs pay the factory to put the radios in the readers and the factory sells them at a low price to small traders who are usually unaware of what they have just bought.
I am suspicious of any card reader - even big stores have been caught out - but I would be very suspicious of a reader used in the escort business. Worst is the fact that, if this did happen, it is very likely that the escort would be unaware of the trick.