Google Customer Reviews are collected from your customers after they place an order on your ecommerce site. When customers reach your thanks page at the end of the checkout process, a popup will appear from Google asking if they can contact them later about their purchase.

If the customer clicks YES they are emailed by Google approximately 8 days later to ask how the order went and about each item in the order. These can earn review stars which Google can then display on Ads. Here's a preview of the Google popup:

Connect this up in Admin > Connect > SEO > Google Analytics > Merchant ID & Enable Google Customer Reviews popup on the thanks page.

Note: These reviews are different to Google My Business which collects reviews about a business or service. Read more