I don’t have hard facts to bring to bear here, but on a recent episode of the Slate feminist podcast “The Waves” (which used to be called “DoubleX” before they changed it so as not to exclude XY transwomen) they made a convincing case that most of the talk of “human trafficking” is just cover for the same old moralistic criminalizing of sex work, and that the vast majority of female sex workers are not enslaved and would benefit more than anything from legalization and licensing.
ETA: Furthermore, if that is what the sting is about, why arrest the johns?