Never mention/or agree to a sex act; never mention/or agree to a price.  As an attorney, I've seen a bunch of these cases.  If the girl is trying to get you to say what specific act(s) you're looking for--she's a cop or an informant. If she tries to get you to say a specific price, she's a cop or an informant. If she says "$60 for a blowjob?", and you assent, even with a nod of the head--they've got you.  Same thing with girls who are suspicious of a client--cops want you to mention or agree to an act and a price. If the cop says: How about $60 for a blowjob?",  if you assent--even with a nod of the head--they've got you. That's why you put the donation on the table--like you intend to pick it up later--and then never mention it again; and if you get ripped off--oh well, better that than jail and/or a convicton.

On top of all that, cops--especially vice cops-- are notorious liars on the stand.  I've seen cops make up whole lines of dialogue they supposedly had with the defendant.  Short of having a secret microphone on you, it's gonna be his word versus yours.  That's why you stay with reviewed, verified providers.  If some ad looks too good to be true, it probably is.