If you are not a regular of an agency, it is a usual practice to collect your money first. Every wolf is treated the same way.
This isn't safe enough for mms. I just heard a reliable story that a wolf suddenly stopped at the middle of the session, quickly put on clothes, snatched his own money on the night table and ran away. The mm was stunt and didn't know how to react. I don't know all the details but there are all kinds of wolves in this industry.