I think NADA value are very high compared to what the market will pay.
In Dec 2013 I sold my 2012 26BH private party. Nada showed a $16k-$18k retail value based on my options, which was odd since I paid $17,500 for it new in 2011. I was offered ~$10k as trade-in that I declined. Listed my TT on CL for $15,500 in about 30 days I sold it for $14,600. Everyone felt the deal was fair.
In Feb 2014, I bought my current TT private party used. At the time it had a NADA value of ~$19k, I paid $16k
2007 Chevy Duramax LMM/Allison
2012 Jay Flight 29QBH
2012 Jay Flight 26BH (Sold)