My current RV was advertised on RV Trader On Line. I was in Sacramento and the RV I wanted was just north of Austin, TX.
Via pictures and a number of discussions on line I was ready to purchase - with the understanding that the final agreement would be after I physically kicked the tires, took it for a test drive, "and" took it to a qualified Ford truck dealership to have it checked bumper to bumper. As to the appliances and everything else that sat on the Ford chassis, I decided to just test myself. The mileage was only 33,000 and the owner didn't use it full time so I figured if things worked for me I would be OK.
The other thing I did to find what I wanted was to just Google it. That took me to many that weren't listed w/any of the on line services such as RV Trader or Craig's List. But it also took me to many that were listed.
BTW, I have also sold 2 RVs by listing in RV Trader On Line - and sold one within 5 days by just placing an ad in the local newpaper (the Sacramento Bee). They have tons of ads every day. On two occasions I tried placing an RV with a consignment dealer. "Never" again. Either by buying or selling, too many 3rd parties have a finger in the deal.
And finally after everything else checks out, I look the seller straight in the eye and ask the question, "Is there ANYthing about this vehicle that you know about that hasn't been brought up otherwise that I should know about before buying?". And continue to look the seller straight in the eye while he/she responds.