It would be cool for character to be able to purchase their own terminals where they would have so much space alotted (like a backpack, depending on the quality of the termial) to place in items they wish to sell. The player could literally take out the terminal and set up anywhere they wanted. Other characters that passed could shop in their terminal as if they were shopping in any other store, and the seller would recieve money as the items were bought.
Sorry if this has already been suggested, and kudos to whoever may have already suggested this specific idea.