This is happened to me many times, where they have a booking scheduled start 10 or 15 minutes ahead of when you knock on the door and they figure they can give you the short shrift in terms of service and time while concurrently making the booked client wait 5 minutes. I also have also received this going the other way, I rock up at the right time and there is a shout through the closed door "come back 10 minutes" or in some cases the provider will open the door wrapped in a towel and tell me the same.
Very unprofessional.
I'm not sure how my regulars manage this, but at some point prior to my set booking time they will flip the sign on the door to say "please wait". When I rock up I just knock and I know I will not be interrupting something, the "please wait" keeps the room empty for me. Obviously there's a calculation here, if the minimum service time is 30 minutes, and the girls are honest and keep to it it means that they will, 30 minutes prior to my start time, flip the sign. This will cost them some business, but I usually pay slightly over their rates for high quality consistent service and so they willingly will do it for me.
Regarding Crystal, I haven't seen her in several years but my visits were always excellent, she was a real trooper and there was never anything to complain about. Maybe it was a bad day for her.
Keep on mongering