I agree with the previous post, everything. Below are some of the issues we have had that you might want to pay close attention to:
The air condition, the air condition, the air condition...Cannot say this enough times. Make them start running the air 1st thing and make it the last thing they review with you, i.e. run it for a long time at a realistic temperature, for all zones.
Check every window for chips in the paint on the outside of the unit. These will rust out if not corrected. For us corrected meant installation of new windows and the techs that did the work took a slice out of one of the decals on the side of the unit.
All locks, they should be easy to open and close, you shouldn't have to lean on your unit to get them to work.
The fan/fans in the bathrooms.
Anything involving water, make sure there aren't any leaks.
Hope this helps. Happy Camping!