My website and AW explain I'd like payment within the first 5 minutes, most do thus without asking. If not I'll usually ask once the clothes start coming off.
Recently had a booking with someone I knew enough about to believe he wouldn't risk trying something on, there were other things around the booking which had lead to some strain. He didn't proffer, at the end both of us fully dressed and ready to go I asked because there was still no sign. He appeared to become a little agitated, asked me do I ever get ripped off by anyone, then didn't know my rate (counted 20 less). It is feasible that he doesn't check my website or AW, because he just gets in touch directly and it has been a few years since he's seen me and then it was incall.
I was complacent in the booking, of I'd taken charge instead of letting him take the lead all the stress points wouldn't have happened. Definitely a lesson.