Conning Johns because prostitution is illegal in the US happens a good deal.
The types of cons jobs described I have seen on US boards go from:
1) The boyfriend (pimp) interrupts you after 5 to 10 minutes and tells you to leave.
2) The girl tells you after collecting the money it is a companionship deal, no contact, what do you want to talk about?
3) The lady answering the phone says she someone has to meet you first; you meet a guy on the street and he tells you to give him the money and he will give you the address. He has a "recent" picture of the girl, who he says is a nymphomaniac and just graduate high school last year. If you give him the money, you get an address of some random apartment and he disappears with your $$$.
4) The moneypak deal. The phone person or girl con herself asks you to buy a moneypak from a drug store and she asks you to give her the number and then she'll tell you her address and apartment number.
5) The total beat down and rob.
Curiously, most of these con jobs are advertised on sites like backpage, etc. and they say no black guys or no black guys under 35. I guess imposing large black guys are more difficult targets, as they may be more inclined to fight back, but they could attract a big white linebacker?
The perps think that since the act is illegal chances are you won't go to police. Many police districts have the policy of prosecuting the more serious crimes, meaning if you were soliciting and get robbed, since the robbery and assault is more serious, they will not press charges against the john who solicited. But there is a problem in anyone assuming this. Some LE are bastards and will prosecute both parties. I have read accounts of both policies.
So it could happen if you do venture out of the "trusted" agencies, as lgna said.