I have no comment on the misdemeanor/gross misdemeanor question. This is a response to and expansion on the discussion about Miranda and how you should respond when they bust in.
A great deal depends on how careful you have been. When talking on the phone, NEVER discuss services. If she tries to do so, hang up. Never discuss rates. If she tries to do so, hang up. If she asks you where you saw her ad, hang up. When you get to the door, use your eyes for a couple minutes before you drop the envelope. Is she moving in and getting close, or keeping her distance and asking you what you want? If she tries to discuss services or rates before there has been some serious physical contact, leave. Once her lips are wrapped around your cock, that's the time to discuss other services.
Although everyone scorns the disclaimers that providers try to use, and I don't disagree, something like that can be more effective for the hobbyist. If LE is recording, and they are, a statement that you need a really good massage because your low back has been acting up, while you move closer to see if she is willing to get physical, goes some way to create a reasonable doubt that you were there for more than a massage. If all the cops have is phone discussion of time, place and duration, with a disclaimer statement suggesting it is for a massage, it is a harder case to win. On the other hand, stating that you are paying her only for her time and anything that occurs, etc., etc., is certainly a waste of time.
NONE of this is enough to stop LE from busting into the room and trying to intimidate you into incriminating yourself. If you get involved in a sting it is absolutely certain that at some point they will do so. It is quite true that they may not give the Miranda if they think they can claim it is still "investigation" rather than "interrogation" but you can short-circuit that. If they don't start the Miranda, as soon as you have identified yourself, name and address and nothing more, ask if you are free to leave. If they say "No" then you have been taken into custody and they are obligated to Mirandize you. If they say anything other than "No" start moving in a non-threatening way for the door and see if they physically restrain you. If they do then you have been taken into custody and they are obligated to Mirandize you. As soon as you hear the start of the Miranda, SHUT UP and stay shut no matter how they try to intimidate, antagonize, wheedle, etc. If they don't start the Miranda, the ONLY thing you do is keep repeating that you would like to leave. If you have kept things clean enough, a smart cop might just let you go once he is convinced you won't start talking. Or, he might drag you down to the station to ramp up the pressure.
On the "busting in" issue, LE likes adjoining hotel rooms with doors between them for busts. If there is no door from an adjoining room, and you chain lock the room door when you enter, they have to do damage to get to you. The hotel doesn't like that. If you see an adjoining room door on a first meeting, get nervous. They aren't all that common any more, and a provider ought to be able to get a room without one. If you like to live dangerously, produce a small wooden wedge and start driving it into the adjoining room door so it can't be opened. If she asks you why, say you sometimes fall asleep during massage and want to be certain of security. If it is a sting she is going to use her safe word immediately, before she is trapped in the room with a suspect.
About physical contact with the lady, if you grab her first you are pretty much done. However, the Minnesota appeals court recently threw out a solicitation bust where the male cop admitted to fondling a provider's breast before the arrest. The court left a loophole by noting it was done without her ever asking if he was a cop or not. It is possible they could hold in future that once she asks if he is a cop, some physical contact is justified to continue the charade. We just don't know. The ban on fondling has to go both ways, so ... NEVER ask her if she is LE. That might give her an excuse to fondle you. If she starts handling your package before you make any move, though, it is probably time to start relaxing. If they then bust in on you, you might exclaim "She was grabbing my penis. Why was she grabbing my penis?" When she is put under oath you can HOPE (no guarantee) that she will tell the truth about who moved first. At the very least, the prosecuting attorney will know he has one more issue to deal with before he can get a conviction. It might be enough to refrain from prosecuting. Don't try to lie and claim she touched you first if she didn't. Never try to lie. Just remain silent.
Understand that you are doing a dance with the provider. When it is a first time meeting, she doesn't want to incriminate herself any more than you do. At some point, somebody has to do something to get the ball rolling. If neither of you will blink, the possibility exists you will have some awkward conversation and then part company. Her motivation is cash. Your motivation is to get laid. Try to keep the little head under control. Good luck with that. My view is that she can better afford a soliciting charge than I can so I'm going to wait for her. But you know, she probably sees it a bit differently.
To borrow some immortal words, Let's be careful out there!