@Haraken: I can't argue that,...but I still try.
Until MC somehow makes sure "his" slave dealer sells those slaves to him exclusively, it's a fault in my plan. Then again those slaves would have ended up somewhere else anyway.
MC would have to visit one place after another and make sure to leave scorched earth slave market wise. Now the dealers hit by MC would go nearly broke instantaneously and wouldn't be able to acquire new goods from slave hunters, which in itself might be a
very bad thing, as they might resort to killing the less valuable captured slaves. I guess MC would have to step in, offer to buy instead and then stab in (the hunters, that is). The dealers would be unable buy anything until they sell their stock, if MC didn't free those slaves while hitting their bases anyway. In that case they have to sell, whom they rented out at that time or have to sell the new slaves of the hunters on a loan/commission basis. After the dealers did that, it is time for an unfortunate accident. When no dealers and hunters are left, it is time for MC to move on.
Money would be removed out of the system and the only businesses that would flourish would be MC's favorite dealer and the dealers and their connected hunters MC didn't hit. If MC makes sure his dealer can't reach his hunters, he has to buy from other dealers. The real problem are the ruined dealers (as long as they are still left alive) and (dealer/hunter)upstarts. The ruined will start to act desperate and recruit new hunters or other new dealers will try to enter their market. MC can slaughter the old hunters in a brutal way, that looks like the demi-humans organized themselves in a way to hunt down the hunters and discourage any newbie to become a hunter this way. New dealers wouldn't be able to buy new stock as the old ones wouldn't be selling any to new local competition, if they are right in their mind. (If they are really right in their mind, they would stop dealing with slaves, because something is clearly out to get him and the hunters. Time to quit I'd say.)
The real problem is, that MC would have to deal with those places fast or they notice something is up. And his own dealer would have to have offered to buy all slaves some time before MC starts his business at that location. In the end he'd offer them their own money to buy the left slaves and kill everyone afterwards. Then the saved slaves would have to travel into safety on their own as MC has to hit the next town asap or this scheme would collapse. (Some of the stolen money could be used to aid that escape.) Next town he can enter the stage with some (voluntary) slaves and the (stolen) money (so he won't have hit (warn) them before, if he doesn't need the money), overcharge the prices for the slaves (, because "his boss (favorite dealer) really needs more slaves"), kill all hunters and dealers, send most slaves home, except those who want to continue to help him and move on. Very soon the kindom or empire or whatever would have him wanted, but that's that. He must be faster than news travels.