The moment to ask
Right after the invoice is paid and the car drives well. Not at pickup while they are looking at the bill; not a month later. The paid-invoice message is the perfect place: 'Thanks for paying — if we did a good job, a review helps a small shop enormously: {link}.'
Make the link one tap
Get the direct review link from your Google Business Profile and use that, not a link to your listing. Every extra tap halves the number of people who finish.
Ask everyone, not just the happy ones
Cherry-picking reads as fake and Google notices patterns. A steady flow of honest reviews, with the occasional four-star and a polite reply from you, is worth more than a burst of fives.
Point the listing at your booking page
Your Google Business Profile's website field should go to a page with your services, prices, hours and a booking form. A reviewer's friend who clicks through should be able to book without ringing.
Put the ask where the customer already is
The invoice link is opened by almost every customer, because it is how they pay. A single line under the total — 'Happy with the work? A Google review helps a small shop: {link}' — puts the ask in front of them at the moment they are most likely to act, with no extra message to send.
The reminder text six months later is the second-best spot. They are about to book again, which means they are already satisfied; 'If we did right by you last time, a quick review would mean a lot' converts a surprising number of regulars who simply never thought to.
What not to do
Do not offer a discount for a review — it breaches Google's rules and reads as bought. Do not write reviews for customers, and do not ask staff or family to post. One honest review a week for a year beats fifty in a fortnight that Google quietly filters out.
Reply to every review
Two sentences, by name, mentioning the car if you can. It shows the next reader a workshop that pays attention, and it is the only free marketing that compounds.