You can look for clues such as caulking and trim coming loose on the outside edges where the overhang and the side walls meet. My Heartland Sundance had to go back to the factory for frame flex at the pin box and that was the first signs I noticed. Also look closely at the pin box area for any markings from trim sliding up and down rubbing the box.
I would be suspicious if it had new caulk in those areas only.
It's a shame that these rigs are built so shabby these days that you have to watch for so many defects.