That is just a conformation so you don't accidentally sell magical or better quality items. If you have better equipment, and don't want to keep stuff to recover an enchantment formula, or something, then feel free to sell them.
After you sell an item it will be listed in the merchant's inventory in a special category if you want to review what you sold (which I try to remember to do if I'm selling a bunch of stuff), but once you exit that session it is no longer possible to get anything back.
