Available only for shoppers in the United States, the product ratings which consist of stars and reviews count will show up in Product Listing Ads across google.com and google.com/shopping. The data will be aggregated from several sources such as the merchant’s website, editorial sites etc.
There’s a good thing and a bad thing about this update. I will start with the bad(fortunately temporary) thing: “In order to give merchants time to share their review content, we’re offering a grace period from late July through October, 2014. During this grace period, we’ll allow product ratings to be shown across all Product Listing Ads where we have product review data available.” This means that if you have bad reviews for some of your products, don’t expect an increase in sales until November because, here is the good thing “after the grace period, we’ll only show ratings for products from merchants who choose to share their reviews with us.”
If you want to know more about the update published today by Google or if you want to know how to enable product ratings on your Product Listing Ads, read the original post on Google Adwords blog.