I will say it is only an extremely stupid prossies will allow you to pay at the end if they have not met the customers before.
They are dealing with very wide range types of customers. How could they know the visitors are not ex-criminals, gang-members, fraudsters, con-artists, etc.
How could they know that after giving the service, the punter will pay and not just drift way using various excuses such as I forgot my wallet in the car, I do not realize that I do not have a cash with me will you wait a second I will come back, or ask to pay with bogus cheque, etc, etc ...
In my personal experience, if you discuss what service is included directly with the prossies before paying it (not via receptionist on the phone) they will deliver those services. In the worst case if they did not you could still do a lot of things (in fair deal of course) for instance claw back some of your money. If they did not tell them I would stay in the room until I got my part of money back. They normally will refund some of your money if you threaten like this as if you stay in the room, they can not get the next customer.