Entrapment will rarely save you from getting prosecuted for prostitution. What everyone has to understand is that entrapment isn't simply the police acting like a client or a provider. So asking someone if he's a cop is literally a waste of time. He can simply lie, and still have grounds to arrest you. To be entrapment, a defense for the crime accused, law enforcement must act in a manner that entices a reasonable/innocent person to commit a crime.
NOT entrapment:
Law Enforcement Agent (LEA): "Hey baby. Looking for some action tonight? You sweet thang you."
John: "Yeah! How much?"
Possibly Entrapment:
LEA: "Hey big daddy. I bet you'd like a piece of this pecan pie. For $100 I'll love you all night."
John: "Do you accept Visa?"
The key is that the LEA must solicit the illegal act; however, if the Client/John is predisposed to commit the crime prior to talking with the police then it doesn't matter. Basically, if you're the type to prowl the streets for a prostitute or have a history of doing so then it doesn't matter.
So if an escort has an add that explicitly implies sexual favors for anything (and I mean anything) of value or a woman is standing on a street corner for the purpose of prostituting herself, then a LEA can initiate the conversation and offer her money for sex, it's not entrapment.
This is not legal advice, but simply the humble words of a well-education client.