Answers to your questions:

What is the chance of getting busted at an AMP?

Nearly zero.  My understanding is that the only way you can be busted is if you request an illegal act for $$$ directly from a police officer.  It isn't too difficult to figure out that the sweet ladies at amps aren't police officers, especially if you become a regular.  (I wouldn't know of course, being the white bread eating bible thumping hippocrite that I am.)  When a place is busted by law enforcement (LE), they usually send the unlucky clients who happen to be there on their frightened way.  They don't have enough evidence to prove you were paying for the act as opposed to a table shower and back massage.  The criminals are considered to be the providers, who are practicing massage therapy without a license and/or practicing the "p" word.  However, keep in mind that depending on the city, your name could end up in the newspaper for just being there at the time, since you are inherently considered a "john".  Usually, LE only raids these places when they become a significant bother to the nearby community.  In fact, these places offer a benefit to the LE.  The keep johns off the streets, and I once heard that one reason that they are tolerated in RI is that the police actually embezzle extra income for themselves from the amp owners.  The amps make so much money that they pay the police to leave them alone.  This is why amps have stickers on their doors saying they support the local LE, and this is why when the last big police convention happened in Providence, there were cops from all around the country in Providence lined up out the door to get their backs rubbed and their glands drained.

I hope this helps......but realize, I wouldn't know about any of this stuff as I'm still a virgin.