Hmm, I probably shouldn't answer, but the original post struck me in a way that I can't let go of easily.
I don't think that ANYONE OWES ANYONE ELSE ANYTHING. Posters that come on with how they have been given a rough time are very suspicious in my book. The second "telltale" tidbit in this thread is the mention of low funds being a reason to call fair repair rates "outrageous" or even the myth of those "outrageous" prices driving us to DIY.
Skilled veterans NEVER treat musicians in need with "contempt" (their may be other types of non-customers that rub them in a way that generates less cooperation however! As a matter of fact, the seasoned veterans (at least all that I know) are usually very willing to help the needy in special ways.
My drive to DIY is based only on my personal interest about how things work and none of my techs have heartburn about it.
Now if we can get beyond the very bogus "contempt" for those making an honest living, there are a lot of resources available for the DIY trumpeter. I took a natural trumpet building course that lasted 5 days. We had three professionals showing us (13 course members) their "tricks of the trade", from soldering to brazing, to making tubes and bells, hand hammering, bending our self made tubes and engraving. In addition, we all had successfully built a working trumpet after 4 days.
The artisans that I work with are very responsive when I ask "Can you show me how to do that". I have learned how to properly change leadpipes, set the gap on a mouthpiece receiver and what happens when we move a brace. They have helped me to purchase the right tools for specific jobs. They have all let me in on "secret tweeks" - knowing that I would not abuse the information.
I know of no website with trumpet repair tips for the DIY scene. The reasons are manifold. No respect, strong differences in the definition of "quality", myths.
So, my recommendation is to look in the mirror. Maybe, just maybe you will see something that could change your relationship with the professionally qualified. My firsthand experience is that they are much more forthcoming than the way you came on in your original post.