Alright, so I'm already assuming that this idea will be shot down immediately, but I thought what the hell I might as well suggest it anyways.

Why not allow users to purchase any item without QI restriction to increase market production? If they don't have the QI that the item requires, simply don't allow the user to activate the item in their inventory, but still let them sell/buy that item. Therefore any player can buy any item, but only the players with sufficient QI may actually activate them in their inventories.

Thank you for your time,
~Matt