Good news!
I was finally able to persuade one of my "slaves" to have sex with me and her willpower crumpled from there, leaving her a willing meat puppet who fervently enjoys whatever my imagination (and the game mechanics) will allow... With that new perspective, I feel like I have some more refined suggestions for your continued development.
Having become better acquainted with your lore, I think there is a fundamental misunderstanding that I brought to the game -- which many others might, as well -- but I think it is easily remedied. From your own material advertising the game and even much of the content within the game itself, I was expecting a sort of hard-edged slavery as practiced by the ancient Romans: a master could kill a slave at a whim and no one would care more, from a legal or moral perspective, than if today you crumpled up a piece of paper and tossed it away.
Consequently, slaves were pretty highly motivated to see their master's wishes fulfilled -- and an attractive (and therefore expensive) female slave brought into the household of a wealthy man and dressed in silks would have no illusions about what was expected of her and would most likely comply as the least painful alternative available to her. Anyway, this was the impression I was left with, based on "buying" characters at a "slave" market.
However, what you have drawn here is much more like a feudal system: it's a contract that two parties willingly enter into and, much like a modern contract, each party has certain rights and obligations -- and sexual favors are not included. To be sure, there is a gross power imbalance between the two sides of this contract, but that doesn't mean that no contract exists or that society will turn a blind eye to people who violate it.
This, I think, brings us to the point of the game you are trying to create... These women, desperate for food and shelter, willingly commit themselves to service (not slavery) in exchange for a safe and predictable life. It's a bargain. Then, people like our enterprising MC in your game come along and try to subvert that bargain by clever psychological means -- transforming maids into lovers and lovers into docile puppets who see fulfilling their lord's wishes as representing the simultaneous fulfillment of their own.
Then our MC can sell that maid's contract -- at a substantial profit -- with the understanding that much (if not all) of her docility and experience will transfer to a new lord after a relatively short transition period (during which, no doubt, many tears will be shed).
And, the best part is, you don't need to make any deep changes to your game at all -- you just need to make more clear what the rules of this world are. Instead of "buying a slave," the MC should "buy out a contract." Instead of a desperate family selling themselves into slavery, they should sell themselves into "service," and so forth...
I think by providing some additional context -- which will, at the same time, serve to further flesh out the lore of your world -- you'll have a crackling game in place that won't confuse players who thing they are buying "slaves." The only minor adjustment I can see you would have to make is that the "slave" assessment center would need to be moved out of city hall -- because it is presumably at least technically illegal to turn your contracted maids into fuck puppets -- and into some underworld setting.
Indeed, such a neutral arbiter of "slave" value could serve as a focal point of conflict between the game's warring syndicates... I'm just sayin'...
Be well!