I would define dating when you're seeing her and you're not paying for any service, but like any other "regular" social interaction, you'll most likely pay for dinner, and if more does occur, tends to be of the civilian BB kind. If you're paying for it, let's be honest, and not call that dating - you're getting outcalls.
Clearly more than chemistry is occurring during sessions, opening the door for an actual relationship. Dating initially is more expensive, because there's a need to balance her lost opportunity cost when seeing you. As things progress, if you're connecting during spa hours, you're usually seeing her outside of her prime time windows, or getting quickies, or getting blow n' go, between appointments. Usually only possible if she's the boss, or has an understanding manager, as time/rooms are money.
Being ok and comfortable with dozens having their way with her per week (or day) is tougher to mentally and emotionally manage and navigate, but in accepting their work from personal, good returns can be had. Yet, there's an expectation of your exclusivity with her, and being ok with that, is harder. Variety, flexibility, and proximity, are reasons for hobbying. Ideally she understands that, and exceptional returns can be had, where you're accessing in ways you didn't know were possible.