I'll throw out one of the most overlooked and yet critical items for buyers.... Test drive it!
I'm not talking a ten minute spin around the block. Take it out for an hour and get on the freeway. Hows the acceleration? How easy is it to merge? What sort of visibility do you have from the drivers seat? Blind spots? What happens when an 18 wheeler blows by you at 80?
Does it handle easily or are you fighting the wheel with two hands. Rollover some railroad tracks, take some steep driveways - does the rear end bottom out? Keep in mind that during any test drive the rig will probably be significantly lighter that when you are actually loaded for a trip. Probably no way around that but think in terms of couple thousand pounds of extra weight and how that will impact the ride and handling.
This forum is full of posts from folks who spent big bucks on a new or used coach and then suddenly they are not happy with how it drives. This could have easily been avoided by a proper test drive. They now are compelled to spend thousands on aftermarket gear to make it better. :S
If it does't drive well before you buy it don't expect it to get better when you get it home.
Good luck!
:C