Welcome to the world as it exists. Usually they just have the word of another cop listening in. These cases generally have one of three results:
After she spends a night in jail, her pimp or madam pays the fine, and they move to another location.
She gives evidence against someone else.
On occasion, the cop is bribed.
In the bathroom solicitation stings, the men accused need not be guilty of anything. All a man has to do to be accused is to choose a stall next to a toilet cop who is willing to lie to get a conviction.
My personal experiences contribute to my opinion. Gay sexual solicitation may disgust me a bit, but it does not frighten me. I have spent a lot of time around gays, including about 10 years in the San Francisco Bay area, and never had a problem with them. On the other hand, a couple of years ago I listened to a cop tell a deliberate lie in court in order to improve his case against a friend of mine. He looked right at the judge and told what I knew to be a lie, and did so quite convincingly. Anything for a conviction.
Just to keep things very clear, I do not know if the cop made a false accusation against Craig or not. Karsnia may have never made a false accusation in his life. My main point is that the potential problems created by bathroom solicitation stings outweigh their potential benefits.