Well they get what they pay for, I always tell them what my standard service includes at the time of booking, before money changes hand. Be honest, dont take advantage of a man with his pants down and dont steal from them. Make you look bad, not to mention your establishment.
"My standard service includes -list of included services- and I also provide a number of extras for varying amounts of money depending on the service, are you looking for anything outside of my standard service this evening?"