Personally, I think its a huge risk purchasing a rig unseen and would never rely on a salesman to be trustworthy. Even if he is honest, there are so many devastating problems that may be overlooked by someone other than yourself, or a friend with lots of experience with RV's.
A salesman's most famous words; Trust me its a steal of a deal, and If I were you I would jump on it....
You really have to inspect an RV to be sure every item works as it should and there is no roof leaks, plumbing leaks, holding tanks and termination gate valves working, window leaks, soft floor, smelly odors, suspension is not worn out, tires are not more than 3-5 yrs old, etc...etc.
It cost a fortune to fix these things at over $100 per hr labor charges, plus parts.
It can sure dampen your spirits to find a number of these problems after the fact.