I don't know if this has been mentioned but it's worth noting:
-If you kill a trader you get all your stuff back that you sold to it/him/her
-I believe they also drop most, if not all of their regular inventory
-Probably is the same with pickpocketing, but I actually haven't tried pickpocketing yet
If you try to pickpocket a trader you can steal all the stuff he sells. Not sure about things you sold him though
