I've never paid NADA for a used car. Always under. Not bragging, just saying. Those values in the NADA books are based on information DEALERS provide NADA. It says so right in the book. There is VERY strong incentive for dealers to provide NADA with HIGHER numbers than someone actually paid.
Am I suggesting car dealers would do such a thing? Am I actually accusing them of doing this? There's very few things in life that I am certain about, but one is ALL used car dealers are crooks. Except those that might be member of this forum, that is!
I don't know about boats, but I don't trust the NADA books on cars. To me, it's the absolute max ceiling price you should pay if you are totally in love with the car. I did that once. I bought a 7 year old Mustang GT with 5,000 miles on it. Mint condition. Never saw rain, let alone snow (I bought it from a dealer, but I called the original owner that was listed on the car's title before I made an offer). I ended up paying the exact NADA book value for it, and while I was driving home, and thinking about the negotiation, I began to put certain pieces together, and I think the dealer was WAY too happy to sell me that car at that price. The car was mint, still had factory chalk marks on the suspension, and even though I paid "book" for it, I'm certain I got screwed on price.
So, just my two cents. I have no idea if this translates to NADA for BOATS or not. I would think so, if dealers are where they get their price info.