Well, in feudal Japan and China, it was common for poor people to sell/place young girls in brothels, when the family didn't have enough money to raise them.
They would be used as maids for the other girls until they came of age (around 14 I think?) and then would work as a prostitute, until someone bought them as a concubine or they died of some STD.
For a lot of girls, it was actually a better life than starving in the streets and end up raped and killed in a back-alley.
Some high class brothels were somewhat respectable.