After reading all the above posts, I still think buying from a private seller not too far away from home is the best way to go. We bought from someone about 30 miles away. When we sell,which may be before the start of next season for reasons not connected with our RV life, we'll certainly start out by advertising in our local paper, which is where we found our rig.
When you talk to someone, like we did, who has owned the rig from new, you get a good feel for how carefully they've looked after it. We were so impressed by the couple who were selling, and the fact that their asking price was about $8K less than blue book, we had no reservations agreeing to their asking price.
The owner's wife was very upset that the rig was being sold, but her husband had developed a disease (maybe MS or MD) that meant they couldn't get too far away from his medical advisors. She was in tears when we drove the rig out of their yard after the sale had closed.