Online retailers are a major source of advertising revenue for Google but shoppers are increasingly turning to Amazon as their shopping first port of call. In 2010 24% of shoppers began researching on Google verses 18% on Amazon, however in 2012 this had almost completely reversed with 30% on Amazon and only 13% on Google. The cost-per-click (CPC) structure which Google uses is much more complex than the commission model which is used by marketplaces. On both eBay and Amazon it is effectively free for sellers to advertise their products with a fee only being paid on when an item is sold. This makes it risk free for retailers to list all their inventory and simple to calculate margins. Google misses out on a massive market by not having a simple to use offering for SMEs. Get the full story at Econsultancy Read also "Google's Product Listing Ads: Adoption, Clicks, Mobile Continue Surge [Study]" at Search Engine Watch