These stories always get me. Because if someone owes you money like rent or a loan of multiple thousands of dollars you having sex with them once means nothing. The arrangement should be, you sell your body to pay me what you owe AND I get to smash whenever during that period. Otherwise you're just losing money.
Uh, ... not sure whether this economic model being proposed will really work. Then again, it could be argued that most readers are here for the "sexy happy fun time", rather than anything else.