The answer is they have a copy of that book regarding gun prices or gun values and that is what they go by.  A friend of mine has a few year old copy and finally I learned where people get all of the outragous prices for the Lee Navies even though though the guns are hacked up, cut down bubba guns.  But, hey!  They are Lee Navies.  They are more rare than Singer M1911s.  Don'tcha know.