Following on from Google's earlier announcement for free shopping listings in Google Shopping tab [webmasterworld.com] in the U.S., Google has now said it's bringing free retail listings on Google Search, first on mobile, and later on desktop.
Initially, the free listings on search will appear in the knowledge panel, and will show buying options for a particular item.

Today, the buying options in this panel are all sponsored links. Starting this summer, these listings will be free. We’re rolling this out in the U.S., first on mobile, followed later by desktop.

[blog.google...]