This assumes that the first party seller is competent, motivated and capable of using their first party documents to good effect performing repairs. Consider the Apple Genius bar for an easy counter example.
edit: may have misinterpreted what you wrote. Nobody should have to have amateurs perform repairs, whether they are first party or not.
Nobody should be forced to use an amateur, certainly. I'm saying that if you can't afford a professional repair, you want the amateur to have access to the best information available, whether that person is you or someone else.
