Selling rare items

Try "Warmaiden's" in whiterun or The College of Winterhold... they usually sell enchanted/rare/random items.

If an item is "Rare" or Yellow labeled, I will sell if it (is of no use to my character or Follower) if it is worth a lot. Otherwise, for low level items that are rare, but not too much money, I will break them down/salvage the item to advance the blacksmithing
options. Some of these items are laughably not rare, but as the game progresses, I have seen some good stuff come through (playing as the wizard).

Breaking down some Rare (Yellow labeled Items) will get you both the bottled Essence and the Teeth. Once you get a fair amount of money, start considering salvaging as much as possible. Really good items of use for you or your companions (non co-op play)
should be applied accordingly, then if you must sell some rare items, try to sell the items of lesser value and salvage everything you can. On occasion, you can even get the bottled essence and the teeth on magic/Purple items. Salvage as much as possible,
and watch your supplies grow so you can make some really great items, level up, and get the most out of your blacksmithing abilities. Eventually you can make incredible items, and if they are of no use, trade or sell them to make up for cash lost from selling
the items originally.

Lord is correct. The more of a particular item they get, the less they give for it. Also why rare games still sell for a lot despite being as old as Abe Vigoda.

This guy sells lock picks, as well as some
VERY RARE items, including Daedra Hearts and Black Soul Gems.