This being a different nation with different rulese that is not essentially how it works. The slave trade is incredibly plenty and it acts sort of like a slave hub. The way slavery works is that the slaves are the labour force, they do all the work and the citizens themselves pay them off for it, it's not supposed to be, but it became a custom. And due to this custom the governing body (The Emperor) made it into a law to tax the slaves for their work, they used to get payed pretty well, but now they're left with enough money to eventually buy a horse, if they're lucky.