My understanding is that some of the very popular escorts in the US or UK manages to do it with new customers and actually can assume the opportunity loss. Also and may be, they have more concerns with their own security in the US than our local ladies in Japan.
Some escorts require on top of a deposit and references, personal informations such as a copy of picture ID card, employers info, etc. Such level of screening actually makes me uncomfortable as I have no idea about the standard of IT security of their website and how safe are infos provided.
I guess they are defining the balance between their security and financial needs depending on their level of activity.