This is an inquiry that has been posted numerous times on different brands. It does not have a usable answer. You will almost hear more griping than praise. Those that have a good unit are not that likely to take time to post on forums how much they love their unit, unless you ask them. The biggest advantage to finding a good used one is if it's in really good shape it's likely most of the problems have been corrected. I would ask to check it over hooked up to full power and tanks with water in them so you can check everything to see that it is working properly. Run the furnace then the a/c for several minutes to make sure they work like they are supposed to and cycle properly. Water pump, 110 outlets, etc. etc. And look it over really close for possible water damage. In the storage areas inside and out. With a flashlight so you can fully illuminate corners, etc. We have has two Keystones and can't complain much at all. First one was used and just needed tires and bearings packed. Current one is new from last September and so far it has been good. Water pump is alittle noisy compared to my last one but I hear that really varies form unit to unit. Ours is under the kitchen sink so It's right there when running. Just take your time and you should be able to tell. Good luck.
Bruce & Sarah, 2016 Keystone Sprinter 319MKS, 2016 Ram 2500HD 6.4L, 1997 Ranger Rebel I/B Jet Bass Boat (not at the same time)
St. Charles, MO.