@John Herold I would start by talking to the mobile home dealerships in your area. You could start there when it comes to finding out more about build quality and the types of materials used in the homes.
You may want to check out a few model homes. The ones that are not built as good will use particle board in different areas of the home. Check underneath the kitchen sink to see what type of wood is there (i.e. particle board, plywood, etc).
Another thing to be aware of is the moving and installing of these homes. Usually, this is where there are issues which tends to happen after transporting the home to the end location.
Many times, dealerships will use the same movers and installers for their homes. You'll want to check the reviews of these dealerships to see how they do with the installation and moving process when it comes to their customers.
Regarding used mobile homes, you'd have to inspect them to see what issues and/or repairs are needed. Many times, issues come up due to deferred maintenance. If the home is kept up by the homeowner and things are replaced on a regular basis, usually it's not an issue when it comes to finding things that need repair.
Though if the homeowner has not kept up with the maintenance of the home (which is usually the case), then there will be many things to fix up and repair. In these instances, you'd have to check things like flooring, plumbing for leaks, roof for leaks, hot water heater, and heating and air conditioning units.
Personally, I've been in this niche since 2007. I've seen a lot when it comes to build quality of mobile homes. All in all, it really depends on how they are built and maintained once someone purchases the home and moves into one.
Feel free to DM if you have any other questions. Hope that helps!