Although it hasn't happened yet I would have no problem with an Escort asking me for a reference when I tried to make a booking. As far as I'm concerned it's the Escorts house so you have to play by her rules. Some guys seem to think that just because they have some cash in their pocket they expect every Escort to be at their beck and call and to be grateful that the guy even considered calling them.
Escorts are running a very personal business that of and as such have the right to choose who they see, asking for references is one way of making sure that they are not dealing with a total time waster or someone even worse when they are in a very vulnerable position.
There is a sign like this on the door of most businesses and prospective clients should keep it in mind when calling an Escort for a booking.