welcome to the world of COMPSTAT. the brass and the lawyers sit in rooms thinking of operations like this in order to get felony arrests. this happens a ton! not just subway. bars, nightclubs, stores, etc...
Problem with this “sting” is it entraps both the guilty and innocent. I’m suspicious about this guy’s intent but it’s possible he’s telling the truth, and there is no way to prove otherwise.
If the cops want to do a real sting, dress cops up as old ladies a la Sylvester Stalone in Nighthawks and go at it.