Reviews
The best moment to ask a plumbing customer for a review is standing right there after the job is done and the problem is actually fixed, while relief is still fresh.
A short, direct request, ideally with a text message containing a direct link sent on the spot, gets far more responses than a generic follow up email sent days later.
A quick, genuine thank you on every review that comes in, and a calm, professional response to any negative one, shows future customers there's a real person paying attention.