Can we add custom stats to NPC's trough scripting? In that case we could adjust the script to add a "suspicion" stat that increments every time you steal something (and increments to the max if the owner actually sees it).
So that, the more stuff magically disappears while you are around, the more suspicious the npc will be so his dialog will change accordingly. You could even make it so the more suspicous he is, the more he will follow you around, up to the point where he denies you access to the store.
It's a pretty awesome idea actually. I think/hope we will see some really nice behavior modifying projects in the future