A bit of a variation on the Mia Noi theme is the "sponsorship" of university girls by wealthy sugar daddys. Sometimes it can mean the girl moves in with the (single) sugar daddy and acts the role of wife and housekeeper. And sometimes it can mean a temporary mia noi relationship (for a married man) while the girl needs money to get through her education.

The daughter of family friends moved in with a much older sponsor to fund her education and I was very surprised at how casually all the Thais (including her parents) accepted it. Their justification was that she was free to leave any time she wanted. Actually, she did leave eventually with out finishing university and is back on the beach helping her mum with the beach chair business as well as hawking her fork part time to the farang tourists.

Sounds like a pretty good deal for the older male sponsors.

When I visited Peru I heard of a similar deal. A (relatitively) rich American hiring young peasant girls as live in "housekeepers" after doing the financial deal with the parents. Then changing them when he tired of them.
The kind of sexual exploitation you get when a country has a huge gulf between the rich and the poor. And the main reason why prostitution in all its various forms is so rife in a country like Thailand.