Google Merchant Centre (formally Google shopping) is the best way to deliver new sales to just about any online store selling physical goods, Google shopping adverts perfect for targeting customers who are ready to buy, they convert really well and you can control the amount that you spend very easily.
When you search on Google for physical products. For example, "Vacuum Cleaners" Google will return the results and you will see the products displayed with an image. When a customer clicks on your product listing you are charged a click through costs by Google, similar to Google Addwords.
The difference between Google Merchant Centre and Google Addwords is that position of your add is determined by the quality and relevance of the feed versus the search term and to a lesser extent the amount your are prepared to bid for the add. This is different from Google Addwords where the amount you bid determines the position the add is displayed. This means that Google Merchant Centre adds are more cost effective than Google Addwords.
Volusion has a built in system for the Google Merchant centre, but has some limitations and we create a feed in excel that can be optimised for the Google Merchant Centre.