The website idea is a good one. Dish should put up a list of all the receiver numbers on accounts with unpaid balances. Even better, show the balance! This would presumably further Dish's aim of getting paid for services by making it harder for sellers to unload their receivers on innocent 3rd parties.
Also, Dish should put up a list of all their leased receiver numbers. This would make it much more difficult for thieves to fence stolen receivers.