The places that keep getting caught with actual human trafficking are hotels, usually not cheap ones, in central locations (so they can cater to "visiting" businesspeople) and they tend to not even change (meaning they catch someone imprisoning and prostituting an underage girl in Hotel X, and then 3 months later they catch another one in exactly the same spot). To me this implies that there's significant police cooperation with the abuse, otherwise why wouldn't they just go by every evening until it stops? And of course, it's the same people in the same space, so definitely the Hotel owners know and cooperate.

So in a way this supports the idea of the red light district: make it legal in a well-defined, licensed space to protect the workers. Because you can't eliminate it and the ways they get exploited in the shadows are pretty bad.