I agree with most of these so far. As I write the story, what seems to work most are 1) Regular checks and 2) slaves as valued commodities, as was said. I also like the idea of thinking of the slave (even treating some of them) as a "pet;" I had written a scene like this already and thought it was cute. This seems to cover most bases without requiring a ton of explanation.

As the story is progressing, it seems to be consisitent so far. It's not a sci-fi or magical setting, so that seems to preclude the "black box" (although that would solve most problems). If I were to use a futuristic device, I would make it the collar; it just seems appropriate.

-As for the issue of lying, yes I agree there should be consequnces to act as a disincentive to do so.

-It seems reasonable that a culture with a "dominant" group would have an strong moral code about how to treat slaves. In this story the dominant group is more defined by social status and birth.

Fianally, I think it's important that the dom believes that they are doing the right thing for the slave (whether the slave happens to be willing or not).