I thought merchant's inventory resets every few days. They may get new items but I've found that any smithed or enchanted items you sell them seems to stay forever. Is there any mod that emptied out their inventory completely before generating new random stuff? I'm tired of scrolling through all those items looking for things I want.

hmm... they are supposed to clear out when the inventory resets, I thought. but merchant inventories get weird sometimes. I looked at the merchant talk page at uesp and there is mention of items not resetting. I have seen this kind of persistent item behavior myself also, although I don't understand how or under what situation this happens.

try saving or quicksaving the game, punch merchant, and reload. this forces inventory reset. see if those items remain.

If an item was in an alias, selling it to a merchant will prevent them from restocking (this includes items added to actors and containers via alias).

You could try buying the entire stock and disposing of it somewhere.