Your customer just let a stranger work on the one system in the house that can start a fire, and they can't evaluate a single thing you did. They don't know if the grounding is right or the panel is labeled. They judge the whole job by whether you showed up, told them the truth, and left it safe and clean.
When the breakers stop tripping and the worry lifts, they're relieved and grateful. Then the moment to leave a review means sitting down and finding words for work they never saw, so they mean to and they don't.
And it matters more here than almost anywhere. For something invisible and dangerous, the next homeowner leans entirely on what your last customers said. Thin reviews give them nothing, and give Google less context than reviews that name the diagnosis, the honesty, and the safe, clean finish.