This is a nice little definition except that it doesn't mean much in the real world. OP could have gotten a better price if he invested some time and sold the car himself. He could have gotten a price closer to his own perceived value of it's worth.
It doesn't matter what you paid or what the blue book value is. You will only ever get what the person willing to pay the most for it that you're able to sell it to will pay. I didn't like it or agree with it the first time I heard it (from someone who ended up not buying a car I was trying to sell) but, years and many experiences later, I understand that it's true.
If he invested some time then he would not just be selling the car as-is where-is. He would be selling the product of the car + his effort which may actually be a net loss depending on how much time he spent and how much of a better price he received.