The mechanic who attends works across engine diagnostics, brakes, transmissions, electrical systems, cooling systems and A/C. That range matters: a mobile mechanic arrives without a shop full of specialists to fall back on, so the person in your driveway has to genuinely know the whole vehicle.
Working on these faults week in and week out builds the kind of judgement you cannot shortcut, knowing which symptom points to a cheap fix and which one points to something serious, and being straight with you about the difference. Every job is handled personally, start to finish.