They way I see it, shops should sell display models for slightly less even if it's never been fired. They buy the guns a dealer prices anyways, so even if they break even on the gun it served it's purpose and they got their moneys worth in my opinion.
"Dealer" pricing is about 10% less than what the customer pays. In other words, the dealer knocks 10% off, and he's losing money. So, what purpose has the "display" gun done besides cost him?