Integration guide - https://support.google.com/merchants/answer/7106244?hl=en-GB&ref_topic=7105160&visit_id=1-636281203285540672-3145339694&rd=1
Introduction to Google Customer Reviews - https://www.iweb.co.uk/2017/04/introducing-google-customer-reviews/
Magento integration for Google Customer Reviews
https://github.com/rafaelpatro/google-customer-reviews