Yes, that's right. It used to be that you pay an entrance fee to the shop and a service fee to the girl. To avoid a trouble in the bathroom, now money is handled by the shop. The girl's share is the service fee received minus a fee she needs to pay to the shop for the use of the bathroom to provide the service. She needs to spend to keep herself fit, healthy and beautiful (hair, nail, cosmetic etc.). I don't think a small tip is a bad idea to appreciate the service if excellent. This said, you don't have to tip, of course.