Definitely test EVERYTHING yourself! Don't take their word for it...whether private sale or dealer/broker sale. Insist on a test drive on the highway. Look closely inside the coach for evidence of leaks. Check the ceiling and along the walls. Check the floors for weakness near joints. Look inside cabinets and around pipes. Make sure the fridge works on both electricity and LP if so outfitted. Verify maintenance records like oil changes and general maintenance items. Check tire date codes....if you don't know how to, then do a quick Google search on reading tire date codes. Tires are expensive and like said earlier, they go bad from age faster than they wear out.
Believe me when I say check everything yourself and don't take their word for it. I bought mine from a couple I've known all of my life and I took their word for the tire dates and several pieces of equipment. They didn't intentionally mislead me, but I found that their perception of working and mine were two different things. Fortunately, I'm pretty handy with most repairs, so I have been able to fix things without a whole lot of expense. Have fun and good luck with your search!