a vendor container is what they need to avoid the items going into their personal inventory.
Alright, I realize this thread is getting longer and some people may not be reading every reply, but still....
Anyways, let's try another approach to track down the issue and the fix. In my current game, there is one default vendor NPC who is wearing a suit of metal armour I sold to him: Contreras at Camp McCarren. Now, he has a vendor container, so unless it is being flagged improperly, something else is causing him to equip sold armour. Thoughts?