I have heard many stories of how the biker gangs and the mafia have control of the sex trade, but is there any real proof to back this up?
I heard of an SP that independantly offered services out of her appartment, one day she got a visit from someone that represented himself a a memeber of a famous biker gang. This "gang member" demanded a tribute to be paid on a weekly basis for this girl to operate her business. Evidently, she chose to close up shop and move to avoid these guys.
Of course, I heard this story second hand.