I fancy myself a pretty fair wrench and good judge of automobiles but the best money I have ever spent was paying an expert to inspect our RV before we bought it. Despite owning 2 RVs prior, I felt I needed an expert opinion. They (should)have a complete checklist so nothing is overlooked and their eyes are not clouded with visions of camping alongside a river in the early summer. It cost me $250 for a chassis and house/systems inspection. It was worth every penny.
Of course I used a checklist as suggested here previously to weed out the problematic RVs first before spending any money on one.