I'm only half way through the book, no mention of debtor's prisons so far.

In many cases the person retained as peon is not the debtor but a relative, typically the daughter. The creditor may also let the peon believe that she will be able to pay her debt with the pay he gives her, like pimps do to prostitutes they've "helped" crossing a border.

By the way, I don't think we need to use past tense when discussing this topic.