Look at the maintenance records and make sure all the periodic maintenance for the chassis, generator and house systems were done. They should be able to show you receipts and/or a log of what was done.
Ask what upgrades have been done, like LCD TVs, flooring, etc.
Look carefully at the paint and make sure there is no paint checking. It looks like little checks under the clear coat.
Talk to them and find out how obsessive they have been in taking care of the coach.
Have an independent inspector or mechanic check it out.
If all that checks out, I would not have an issue purchasing the coach.