I (American) started an extremely similar VC-backed business in Germany. We were focused on car maintenance and detailing, but otherwise we had the same business model that you describe: our major selling point was upfront, fixed pricing without a diagnostic appointed, supplied by a network of independent mechanics and backed by a guarantee. We also had a sister company who focused on home services, although their initial market entry point was paint jobs.

I think this is a very viable business model that can provide tremendous value to consumers. If you guys want to chat, shoot me a DM — I’d be happy to share my experience.