What are you doing to your car that requires such a close relationship with the repair shop?

Responsible (directly or indirectly) for quite a few of them, mostly oldish and wheezy; I’m not myself mechanical; and we use the shop mostly for routine maintenance—rotate the tires every few thousand miles, swap the brake pads, deal with the oil changes/fluids/filters, etc.

Partly as a preventative measure: we trust them. In the rare cases when they find something, it’s real. As a consequence we get ahead of brewing problems.

Plus loyalty, to some extent; we try to throw work their way when we can, even if we probably could handle it ourselves. The relationship between our families goes back a good 60 years by now.

Fully grant that my situation is unlikely to be representative. And no shade toward OP—it sounds like a cool project thoughtfully done, and a real improvement over the status quo for her relative!