Yep, can't tell you how many people I've seen come into dealerships with a printout from NADA or KBB, thinking they'd get "average" book price for a trade. I tell them, Look at "rough" and then subtract some from that. They aren't going to give you more than what they could buy the same car at the auction for.You're right....dealers use the Black Book, a dealer only publication, updated weekly via latest auction sale prices.
If you can ever get someone to take you to a "real" dealer auction, like Mannheim auctions, you'd be very surprised how cheaply vehicles get sold for.....opened my eyes.