Recruiting through slavery (Kenshi)

How do you know, with some probability it is possible to turn a slave when buying, if you buy it from a slave trader, so, is it possible to buy a fog that he would join you (for example, he was caught by slave owners and not a player), or you can attach to himself through slavery only those Nps, which are sold initially by slave owners?

It's just that there's not a lot of info on the forums on this topic, and it's not clear if it's possible to do so.

I know about the mod Recruit Prisoners, it's just a little different.