Some of the let's say more experienced girls don't mind as they've been asked so many fcuking times for it they go for it. You're paying, she's providing a service.
No, you don't pay anymore that you would give her in the morning anyway.
Very infrequently you may even be asked to go there! Problems in the old 'Wizzards Sleeve' spring to mind!
Sitting in a bar and asking them if they will isn't advised but I've seen blokes ask!