Okay, This is not yet confirmed to be done in 1.10.2 because I remember in patch 1.8 or 1.9 my friend duped his epic boots.
1. Put an item in one of your key binding spots
2. Make sure you are wearing it.
3. Head to a vendor and right-click on the item which sells it.
If it still is able to be done your item will still be in the key binding spot and you can sell it over and over again.
P.S. Don't get mad at me if it doesn't work i'm just telling you guys so you could try it and post what happened.