I recently accidentally sold something of large value to a vendor when mass-selling similar items, and didn't notice until it was too late. Many games feature an option where a vendor will hold the items in a cache for you to re-purchase for exactly the amount of money you sold them for, in case you experience seller's remorse or make a stupid mistake.

This, or at least some kind of prompt when you're about to vendor an item with a UV. Sure, completely geared toward people who make stupid mistakes sometimes, but it has a place!