Actually, you have the Blue Book, Red Book, and Black Book...
The Blue Book lists the "accepted" value of a particular car based on several catagories. Rarity and Desireability are only two of the benchmarks. This is the Book used by the Insurance Industry because it lists the Lowest Value.
The Red Book is the one the Dealerships use to establish the sales price of a car, and that price can be modified by conditions...for example, a $50,000 used car that has dents, dings, and extensive body rust would probably sell for less than $20k, despite the fact it is listed as being worth more than double that.
Then you have the Black Book, which not too many dealers have access to, that lists the "actual" value for said model of car in good or better condition.
In any case, as with in other industries, the books are a GUIDELINE only. Consider them a Starting Point and not an End Point.