I don't pay in advance. Read and heard too many bad stories. All my past bookings none asked for payment upfront.
I usually bring it up prior to booking that they will be paid, in cash, after our session is completed. With that being said, over the last few months guys I'm interested in mention they only take payment upfront when I bring it up.
At that point I just move on. But it is annoying since like I said, it's been happening a lot lately.
Still hasn't happened yet. I actually thought this would happen often, but nope!