They're getting the customer that has just started and doesn't know better. They see a clam, shrimp or a nice piece of coral and the sales guy tells them they could have it in their tank with no problems, and the price is usally very cheap, and the customer buys it. As long as they turn over the stock, and some corals and inverts do last for awhile before they die, they'll keep on getting them. If they don't they would carry them anymore, just like the Petland by me no saltwaterfish. You can get some good deals from these places, and since they want to move things you can even bargin with them, but you need to be very careful.