Google will add ratings to its product listing ads, which are used by merchants to sell products via Google search pages. Such ads appear in comparative grids of search results, and Google said U.S. shoppers will see ratings of up to five stars and a count of reviews below each item.

Google said the rating system is based on aggregated rating and review data from multiple sources including merchants, third-party aggregators, editorial sites and users. But it remains unclear how many merchants who gather customer ratings will decide to share that data with the Internet giant.

"Product reviews provide critical information to shoppers making purchase decisions," wrote Mike Capsambelis, a Google Shopping product manager, in the blog post.

Merchants that want to run product listing ads are already required to provide real-time price and inventory information to Google as well as images of the products themselves.

The more data Google displays around products, the more its search results resemble what users find when they search on Amazon. However, Google still can’t match are Amazon’s fast delivery and one-click ordering.