As stated, If the owner has to dig or him-haw around for answers to basic questions about the trailer - beware.
1) Stand at the back or front of the trailer and look down the length.
- Do you see wavy walls, or bumps in the wall? This could be a sign of delamination.
2) Look under the trailer.
- Look at the frame for bad rust or broken welds.
- Look at any exposed wiring or plumbing for possible breaks or frayed wiring.
- If the bottom is not enclosed, look at the Floor of the trailer for any water damage.
- If it is enclosed, look for any "access ports" that may have been cut into the Coroplast to gain access to the items between the floor and the plastic.
- Look at the backing plates on the wheel assemblies. Check the wires for bad or cracked wires.
- Check for grease or oil on the bottom side of the backing plate, it could mean that grease has gotten past the wheel bearing seal and contaminated the brake assembly inside.
4) Look at all surfaces where the walls connect.
- Corner joints - missing screws, bad/missing caulking
- Where walls have holes cut in them (Windows, water/electric access, etc). Make sure that they are sealed on the TOP side (Some windows have been found to not be sealed on the top but were on the bottom - creates a nice water access point)
5)Roof - Check All the caulking points (roof edge, Anyplace where something goes through the roof, Etc). Water can come in one place and damage someplace else.
6) Floors.
- Walk around the entire floor of the trailer. "Feel" for any give or soft spongy spots. This could possibly mean that the floor is coming apart. If you are not heavy enough, take someone with some heft and have them walk on the floor. Check near the Kitchen, where the floor meets the wall, over the Wheels (possible water intrusion from tire spray), bathroom...basically the entire floor.
This list is no where near complete, but it will give you a start. If you find any of these problems in a 2-3 year old trailer I would avoid it. Unless you are Bob Villa and you can get the trailer for chicken feed...Heck, I would still avoid it.
YMMV, Check your dealer for details...Just my 2 cents.