I think market stalls kind of collapsed the entire economy within the game. Everything is dirt cheap, and part of the problem is that anyone can buy from anyone in a safe place for everyone. So this might be an entirely stupid idea, but can market stalls be set so that if the owner is demonic, the other two circles simply cannot buy at the stall? Leave normal shops alone, to allow the thrill of breaking into enemy land and buying forbidden things. Making market stalls only sell to same circle people might actually result in prices raising somewhat, giving us a place to spend gold again.
Or its just a really stupid idea. Who knows.