Car Auction Prices versus NADA/KBB?

Question by Al: Car Auction Prices versus NADA/KBB?
How do car auction prices vary from KBB or NADA pricing?

For example, lets say you have a recent model year car with a NADA dealer price of $ 15k, and a trade-in price of $ 12.5k, what price range could a dealer potentially get the car for at auction?

I'm trying to determine what the potential markup is for these cars as I shop used vehicles, to best enable my negotiating. I want to be reasonable and let dealerships see a profit, but I

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