KBB is the defacto standard for dealerships and lenders in Ca. Certain model vehicles are not worth book. Just ask any dealer who paid wholesale KBB, then has the vehicle in stock for 4 months, having tried repeatedly to retail it, as well as get his money back thru the auction, as he frustratingly watches similar vehicles sell for $3000 less at auction. Maybe that will help some understand TMV (true market value).
A classic example is large domestic SUV's. The new ones are not moving well, so the used one are worth less....some as much as $5000 below book.