Can you imagine what the girls would say if punters asked if they could send a cheque in the post a couple of days after the appointment, they'd be up in arms, quite rightly too. Same goes for paying up front, no chance.
It has to be cash on the day, either at the start of the appt. or at the end depending on how well the girl knows the guy.
I once left my wallet in the car and had to dash out to get it before the next punter turned up, but that's another story.