Excellent question, shlishi, to which I don’t know the answer. Try sending it to one or more of the email Choshen Mishpat services, and kindly share the results. I know a mumcheh in C.M.; I’ll try to ask, and share the answer (but not to be relied on for halacha l’meisa, of course).
I’ll also take my own guess first; that it depends on what normal practice is, as well as (in the first case) whether the maintenance was required anyhow.
IOW, for the first shaila, the answer might depend on:
1) If standard procedure is to clean the rotors as a first response. If so, since a mechanic is not a navi, he may be entitled to compensation, and,
2) if the rotors needed cleaning anyway, that might be an additional factor.
For the second shaila, it probably depends on whether most consumers would assume that the mechanic would do the more expensive job without asking, if the difference is not great. Besides, if you needed the more expensive tires, you would have agreed anyhow.
I think he still should have called you, and possibly, if it was his error, honored the cheaper price anyway, but I don’t know if there’s any recourse.