It's very small, just from my own experience and the experiences of the women we have supported.
I personally have counselled over a thousand victims of sex trade and sex trafficking, and these are the stories I'm hearing. If they want to work in a particular strip club, they must perform fellatio to the manager or the owner, and if they don't, then they can no longer work there. I heard the same with a massage parlour not too long ago, where a massage parlour owner had HIV that was not disclosed and he was having the masseuses there perform unprotected fellatio if they wanted to work there.
Those are just a couple of examples. Most of the pimps I have known have moved up on the ladder. They may have started at the lower scale of things on the street, moved up with the money they gained off the backs of women, and opened up escort agencies and massage parlours. Just giving these guys a business permit doesn't turn them into good, honest businessmen. They still use the same abuse tactics.