If you really want some fun, try pricing a motorcycle or boat through NADA....the prices are no where near what the vehicles are actually going for.
I don't know how these sites calculate values....could be depreciation schedules, or links to actual dealership transactions? I know if NC - no one would know what I paid for a used vehicle from a private party. When I go to register, the DMV doesn't even ask what I paid - they just use a value that I think is based on a depreciation schedule. Gone are the days where people ask you for a bill-of-sale that shows thousands less than your agreed upon price....
Dealers are in bed with NADA...funded by them. KBB is independent. Just for S's and G's I requested value for a '13 Cruiser with ~ 115K. I got back an estimate in the high $30K area. Got phone calls from 3 local dealers, Ford, Chrysler/Ram, and Toyota. Toyota/Lexus store locally did not respond.