Though I've worked on a ton of stuff, the above is where there's A) enough people owning the above who still think all vehicles explode when their odometer hits 100K B) have inexpensive and easy repairs for simple things that are rotting or are wearing out and C) plenty of people who know better and when they test drive a 10-year old one that feels as good and looks as good as new, won't even negotiate your asking price.
I've entertained the idea of selling BMW M cars, Audi S/RS and Merc AMGs, but the reality is there's far more labor involved, far more to usually fix, higher acquisition costs, less demand, and buyers who are completely insufferable. I've sold several, but in retrospect it wasn't ever worth the time and effort.