FWIW I have never paid anywhere near NADA value for anything but can't ever remember selling anything at or below NADA...
The point.... NADA is intended to be average....I am WAY better than average at finding a deal and maybe just a little above average at getting a good price when selling...
Of course most of the things I have are in above average condition when I sell them and not always but sometimes need work when I buy them.
A couple years ago I sold a 4x4 atv for over double it's book value but while it had a couple dings, mechanically it was better than new...
boats can be the same way.... Two identical boats that book for $8k .... One w nothing special, poorly maintained, and ratty might be worth $4k while the other w great electronics, various upgrades, garage kept, and meticulously maintained might be worth $12k