It appears that Google is now ranking products by their ratings in some Google Shopping results - the sponsored results that appear either at the top or on the right of the search results page.
Here's "best samsung phones":
Here's "best sony tvs":
Curiously, there doesn't appear to be consistency if you use the word "best" or "top".
Here's "top sony tvs":
Why does it change?
According to Ginny Marvin at Search Engine Land, the feature is just a test. Give it a try, and see if you get the rankings on any queries.
Images via Google