There was a Chinese restaurant here in Nevada, actually a couple owned by the same woman. They were sort of the typical dine and dash $7 combo plate kind of places.
This was years ago when I used to deliver for a produce supplier.
Anyway, she always had a kitchen full of workers. 5-8 at anytime in a small kitchen, working away. None of them spoke a word of English. I thought it was strange and wondered how she could possibly be making money with that sort of labor. It finally dawned on me....as the entire would switch out ever 6-8 months, that they were probably not being paid. I figured they were working off debts to get here.
Massage places seem to be the places doing this sort of crap now. I have noticed a bunch of the little strip mall, shady looking massage joints spring up around town. Like 8-10 or so in a row of only 200,000.
Back home in Ohio there was an Asian family that lived across the street and a couple of doors down. They owned 3 nail salons in the area. My ex used to go to one and had commented that only a couple of people were there all the time and the larger part of the staff changed at about the rate you are describing. I think it was from work permits only being for a short time. Business owners may hire companies to help them find these workers and help them get temporary work permits or if the case of some business owners they know how to handle it themselves or have an employee that did it for them.
They made great money in tips, who knows what they got paid hourly. She had found out a little bit from conversations with the guy who always did her nails, he was there full time all the time and spoke English well. A big portion of the money they made was getting wired home to family members or to a spouse.
The guys working in the kitchen were probably paid under the table and were also sending that money home.
Massage parlors seem to run the gamut from full time staff like the one in the plaza I worked in that I described, to workers being shuttled in and out like a nail salon, to the worst possible thing which is of course sex slavery.
Anyway, we haven't heard anything else about this sex slave business so far so they either have a mountain of evidence to sift through or these peoples lawyers are slowing the process.