One thing I have noticed between manufactures is in how the wall structure is constructed. With most that I have seen they start with a typical aluminum stud frame and laminated exterior. On mid to higher end trailers I've seen the use of gel coat exteriors and sandwich wall construction that's compressed together on a roller machine. No worries about delaminating.
When we were shopping for a trailer one thing my DW was fixated on was cabinet construction. She was tired of the lighter weight trailers with drawer slides and hinges coming apart. On some trailers when opening the cabinets or drawers you could see considerable flexing of the main cabinet structure and the slide supports were plastic with only 1 or 2 screws. On other trailers there was no flexing on cabinet walls, very solid and slide supports were metal with 3-4 screws.
Things I noticed on lower priced trailers were mostly cosmetic. Wiring in exterior cabinets were not bundled and tied up neatly, often hanging loose making them easy to snag when loading/unloading items. Slopping caulking inside and out was also common.