Reviews are the single biggest thing that decides whether you show up above the other guy on Google. The best moment to ask is the day you finish, while they're still standing there with the hot water back on.
We'll write the message. You send it from your own phone — a text from you gets answered, a text from a system doesn't.
People who left words on your review page. Nothing appears on your website until you approve it — and only if they ticked the box letting you use it.
Who you've asked, and whether they opened the link. Nobody gets asked twice by accident.