you'll find a hell of a lot of dodgy listings on backpage, especially the Chinese / Japanese listings.
A lot of those are girls who've been tricked into it.....came across one recently
She flew into Heathrow for a holiday, the "friend" who was supposed to meet her never showed. Instead she was accosted by a chinese bloke who offered to help. Stayed with him a few days, then he took her to a bent chinese gambling den where she was helped to lose $8,000 - she didn't understand the numbers she was dealing with. The guys at the den "suggested" she work her debt off, took her passport and sent her up north with a male pimp to keep her in order. She was beaten, starved, her clothes locked up. Eventually they also put her on AW and Vivastreet, however relatively few of the Chinese girls get listed there as they're too visible.
From what I've further discovered it seems likely that a large proportion of Chinese and supposed Japanese escorts are working under similar circumstances
for the girls safety I'm not going to post links