The book value is only a guide. The market value is what is owed for the vehicle. Also, the retail book value is for a vehicle detailed and ready to sell. Very few vehicles on the road are reconditioned, detailed and ready for resale. If you take the retail value and make an estimate to make the vehicle ready to sell, you generally come pretty close. However, when the market is in flux either high or low, the book value is based on history and will not be up to date with current market conditions. Big vehicles are overvalued and small vehicles are undervalued in the books.