Google Shopping will become an entirely commercial model from June 11 this year, according to the Inside AdWords blog.
The transition to a PPC model began in February, when product listing ads were introduced to Google Shopping.
Product listing ads feature large product images, and are triggered from a product feed in Google Merchant Centre.
Merchants have to pay Google every time a searchers clicks their product listing ads.
Since the changes rolled out, retailers using product listing ads have seen lower click-costs, higher clickthrough rates and better ROI, compared to traditional Google AdWords text ads.
However, Google staggered the transition from free Shopping listings, so retailers weren't initially paying for every click from their product listing ads. The search giant said it would complete the full transition in summer - and has now announced that June 11 is the day.
From then on, all Google Shopping results will be paid for by merchants. Searchers using the service will be presented with clear product images, prices and sizes in the search results. When they click an ad, it will take them directly to a sales landing page to buy the product.
Because of the large images and clear product information, the Shopping search page becomes much like a 'marketplace' in itself: consumers can compare products directly within the search results, then click the item they wish to purchase.
Commentators originally said Google may be trying to make a move into Amazon's territory with the changes to Shopping, by creating a global marketplace where multiple traders offer products and services from a single marketplace.
In the US, the changes were initially introduced in November 2012. Early reports suggested product listing ads were more efficient for advertisers than traditional AdWords campaigns. Marin, Adobe, RKG and Kenshoo all reported positive uplifts in clicks and conversions during the first quarter of product listing ads in the US Google Shopping results.
Google says 300% more ecommerce sites and retailers are now using Google Shopping, and those with product listing ads have seen traffic increase by 20%. More than one billion products are now being promoted on the service.
In the first month after the change in the UK, ClickThrough Marketing boosted Google Shopping ROI by 54% for retail clients using product listing ads.
ClickThrough has also produced a Google Shopping white paper with more information on product listing ads and the commercial changes to the service.
Internet Marketing News from ClickThrough - the conversion rate optimisation experts.