Setup and bust happen in a hotel, much more often. They will have undercover ladies, and as soon as you talk about "doing it for a price" wham you're busted. You thought you were getting a bargain, haha, if it is too good to be true.
A spa, is different. They will send in undercover male LEO, to get the lady to offer X, Y or Z for $$$. They will most likely record that as evidence. Now if you happen to be in the next room when this happens, humping and bumping like a buddy rabbit. There really isn't anything to worry about.
I have been in a spa when something like this happened. The reality is as long as you keep your mouth shut, and the AMP girl is going to keep her mouth shut. They don't really have any evidence to bust you with. Okay you were getting a massage and fell in love and started doing it. Maybe the 2 of you are dating? There is ZERO proof that any money was exchanged for the act.
Again, don't get scared because the LEO told you unless you confess to everything, your life is over. It is a lie. You'll do better if you forget how to speak English. Let LEO get mad and yell and scream at you. They can put on a dramatic act. You're still innocent until PROVEN guilty.
The odds that LEO is going to bust a spa and clear it out and put all new girls in there just to bust Johns, is rather impossible. Speaking for myself, if I saw all new girls and a manager in a spa that I usually go to, I would get very suspicious very quickly. Especially if they started asking me strange questions about what i wanted and how much I was willing to pay.