Factors

"Back of book" means buying below Kelly Blue Book's lowest trade in value.

Dings, dents, worn tires, and mechanical problems are all estimated and deducted from that figure. The wholesale appraiser (on trades and at auction) usually goes to the auction site and shops that particular model to see the average price it's fetching in the wholesale market.

These sites require a dealer number to get into, so if you have a friend in the business, you might be able to get a peak.