Google's Head of Shopping recently sat down for an interview with AllThingsD, during which he expressed that Google wasn't interested in becoming a retailer. He explained that the acquisition of BufferBox was for other retailers to use to level the playing field, rather than for a future Google retail operation.
Sameer Samat, Google Shopping's VP of product management: "We aren't planning on being a retailer. We don't view being a retailer right now as the right decision."
And about BufferBox: "We are trying to provide a level playing field for retailers."
AllThingsD points out how some of Google's Shopping pages have become somewhat Amazon-like in their appearance. Nevertheless, Google maintains they aren't interested in becoming a retailer. Google is continuing to change and tweak the shopping experience, such as now requiring companies to pay to have their products listed.
That change has prompted Microsoft to run the "Don't get Scroogled" campaign against Google. Of course, I wouldn't rule out Google becoming a retailer in the future. They have lots of consumer data at their fingertips that they could put to use. It's just not in the cards quite yet.