Well, here is my experience with a recent NADA sale...
We previously owned a Casita tt. NADA had it (year, model, etc) near $7k... however... because I frequented the Casita Forum website, I learned that the resale value was much higher than the NADA figure. Because of that (make specific) forum, we learned that the demand was high for these little fiberglass tt's that could be pulled safely behind a mini-van! The value of my $6,900 NADA quoted tt was actually $10+k on the current market due to demand (of course the brand new 2009 ran for many,many thousands more which was a plus for late model resales). We actually sold our little 17' tt for about what we purchased it for used two years prior.
God Bless site specific forums!