With Google Reviews you can easely add the Review Popup and Badge to your OpenCart Store.
All what you need is this Extension and an Account in the Google Merchant Center.
Once enabled, this extension does all for you to collect Reviews about your products from your customers.
Customers will receive an Email after a few days - if the agreed to receive one after made the order - and can comfortable make the Review.
Increase the amount of real Reviews from real Customers and benefit from better Search engine Rankings and Sales.