Work with a honest dealer, check their history. Along with all the things you have heard in this thread, insist on a a detailed checkout by dealer. check maintenance records with the trailer. Many roofs have a limited 12 year warranty or less but this assumes proper annual maintenance. the tires and batteries, depending on age will need replacement. appliances normally have a 2-3 year warranty so detailed checkout is necessary, the seller should be sensitive to your concerns and willing to work with you if it is a good quality unit.