That has yet to be decided. That's the problem. In a reasonable society, of course, no one would question this. However, while driving down the road, a shoddy repair has an effect on another system which interferes with the lane change sensor and allows you to drift into a semi while checking you iPhone, that is Tesla's fault (or so you'll argue in court). Things get into grey areas quickly. Also, if you have a lawyer that's worth his/her salt, they'll try to suppress the fact that you had a repair on an unrelated system by an unlicensed shop.