Hello,
I have a small complaint regarding the merchants that keep in their inventory your old epic/legendary/unique items.
It is a good idea to allow the player to re-buy an item that he sold "by mistake" but when the merchant keeps an item with a level under your own, it gets tiresome to browse their new items while being spammed by old underleveled gear you sold and you will never want back. It makes shopping a bit tedious.
If it is a gear level under your own, they can just delete it for good. Even if it is a unique item! You cannot sell a unique "quest" item anyways so there will not be any problem.