You might read this thread
Former rental motorhome threadMost of us are very happy with our second hand motorhome. We bought our former rental class C from a reputable dealer, though we didn't know that at the time. The only bad part was an attempt by the dealership accountant to sell us a warranty. I turned it down; then a guy I knew in the service end of the business told me the warranty was useless. In 9 years it hasn't visited a garage or RV dealer for any work other than new tires, so even a good warranty would not have been useful.
I was a complete amateur with RVs so could easily have been sold a lemon. Make a friend with experience and knowledge or hire one to accompany you when you find one you like.