If you want to buy a used RV you should make it a hobby of looking at all sites and lots in your area for the style you are aiming for. You will start to see the scams at a distance. I use search tempest on my PC browser set it up for a nationwide search and look at everything available on craigslist. Select all USA, for what you put in what you want to search for, category is sales/wanted, subcategory is Recreational vehicles then go for it
You aren't going to travel all the way to the other side of the country to buy, but you may see a pattern in where certain makes and models are available. Its fun actually.
You can search for pretty much anything for sale on craigslist this way. I would be careful buying any vehicle without a complete inspection.