If you want a concrete example of what I'm thinking, remember the farm doggo in Corruption of Champions? Look at the text for the scenes where the "Hero" slowly corrupts her over time, it's SO worth it. Something like that. I always make sure to play that when I go back and create a corrupt spellcaster for the sake of enjoying scenes like that.
Further material for this is in that game, Free Cities. If you play your cards right and are as nice to your slaves as possible (so they gain max trust and max devotion), then adjust your arcology accordingly, the result is preeeetty much what I had in mind.
As a result, I think such a slave owner (either as an active slaver or simply a buyer) wouldn't just let people have access to their property, even if they're doms. They're eyecandy, the cream of the crop, the best of the best, meant to show off the owner's status, wealth and/or training ability. The wares you'd put in your shop's window to advertize what you have, "look but don't touch" samples, if you will. And what such a person sells is essentially....duplicates (as in, other slaves of the same species/with the same mods) or merchandise (like dolls, onahole and cock replicas). I'm really thinking high-end luxury slavetrade here, something I'm convinced exists in the underworld of the TiTS-verse, especially on the fringe.