no, it's the nature of the used car market. If you trade a BMW into an Audi dealership, more often, it'll get recycled into the dealer auction system, then to be picked up my other independent dealers. If you trade a BMW in to a BMW dealership, it's more likely to sit on a BMW dealer lot for a longer time.
Basically, if you were a used car dealership, you would go into the auction peroidically, pick up say 20 cars, put them on your lot, then 3 months later, anything you don't sell, you send them back through the auction for a new set. That's why you see different cars on the pre-owned lots all the time. It's not that they were selling it like hot cakes to customers, they're just recycling their inventory.