I've bought two used truck campers and three used 5th wheel rv trailers through dealers. Same with buying used equipment and agri trailers.
Most dealers around here will give you a 30 day warranty if pressed on a used 2-4 year old units they have checked and serviced. If they don't I walk.
Buy from a individual and its yours when you pull out of the driveway.
I've bought a lot of used trucks and trailers (rv and non rv) for my business and RV use since the late '50s.
If the dealer wants to sell his unit he will have to deal if pressed.