I don't know why but, what I did when I was looking to gauge a good deal was look at the NADA, and not select any options. If it was in the low retail range on a unit without issues, I considered that a good deal.
The last two campers I was able to get it below the low retail number without options selected and I really got a great deal on them.
I have noticed that numbers are all over the place though. Not sure if you are financing or not but, that will play a factor too. Depending on who you finance through they will verify values to ensure they are not obviously loaning more money than the camper is worth.
Do a search online on rvusa.com or rvtrader.com and search for that model. See what the price ranges are. The majority that will come up with be dealers but, you can still get a rough idea. Obviously, if a private party is charging as much as a dealer, it's probably not priced exactly right.
Good luck and welcome to the forum!
2012 Keystone Sprinter
Still sticking around for the good people and advice.