My sister worked for a car lot for a short time,and in their training they taught them that "blue book" values were a joke.
They loved when people come in talking about "blue book" values, those people usually paid a lot more than they should have.
You don't even want to hear some of the other stuff they taught them! It was bad, really bad. She only lasted a few months there!
Really, any item car or sewing machine is only worth what someone is willing to pay for it. Finding places where they are sold, and what people have paid for them is more accurate that something someone put in a book.