You can find gently-used campers and RVs for sale by their owners on specialty camper classifieds sites, such as RVTrader and RVSFSBO, as well as on general classifieds sites such as Craigslist. Auction sites such as eBay also frequently contain listings for used campers sold by owners.
RV Trader's website features a special section dedicated exclusively to listings created by private sellers, compared to other sections of the site that contain listings from dealers. Each listing on the site contain pictures of the camper as well as a description of its condition. While many listings may say that a camper is lightly or gently used, you should always examine the included pictures to look for any signs of excessive wear or damage. If you still have questions after examining the included photos, you can also contact the seller and request additional pictures or a video of the trailer, though sellers are not obligated to comply with any requests.
Sellers posting on Craigslist are not required to include pictures in their posts, which means it can be difficult to tell how much a camper was used. If you arrange to meet a Craigslist seller in person to inspect a camper, make sure to do so during daytime and bring a friend along to avoid potentially unsafe situations.