Not sure if something like this was mentioned before, but due to the fact that you can hardly do something with your household slaves: What about making your most martial slaves gladiators like the slavers in Mereen do?
It could look like this:
A slave trader can build an arena either in his cities or in his family palace.
If he does so he gets the slave management option to search an oponent for his slave gladiator.
If found he suggests an money amount for the bet and both slaves fight like in an battle duel. The loser is either wounded or maimed or killed and the winners master gets the money plus some prestige
It could look like this:
A slave trader can build an arena either in his cities or in his family palace.
If he does so he gets the slave management option to search an oponent for his slave gladiator.
If found he suggests an money amount for the bet and both slaves fight like in an battle duel. The loser is either wounded or maimed or killed and the winners master gets the money plus some prestige