As it is, you cannot see, once in-game, what those items are... unless you have the said item in your inventory. This means that, if you have nothing the shopkeeper would want to buy from you, it'll show up blank; giving no useful information to the player.
What I propose is a config option that allows you to do that; OR, simply having it always show everything, regardless of what you have in your inventory. Set the QT to 0, and block it if you don't have the precised amount. It'll be much more useful like that.