I think you can tell it easy, based on price and how beautifull the girl is: why would a nice girl work for an agency who charge 100£/hr if there's plenty of agencies who charge 200£-300£/hr? I'm sure most of them will be happy with 2-3 clients a day for 200£/hr instead of 4-5 clients a day for 100£/hr. Or do you really think they are stupid to work for 100£/hr for full service?