E-Commerce tracking lets you monitor the cost per sale of every transaction
E-commerce tracking is the ability to log the sales on your website (as well as which keywords and URLs prompt them), and the corresponding cost data. Unlike conversion tracking, which allows the user to view a cost per conversion, e-commerce tracking allows you to see the cost per sale.
With e-commerce tracking, comes enormous scope to see the success and failures of your AdWords account. You can calculate a return on investment (i.e. the revenue you generate, relevant to how much you spend on AdWords), learn the value of an average sale and the time of day which the most sales are made. E-commerce tracking works in the form of a code that is embedded in to the website.
E-Commerce tracking code should be installed by an IT savvy person
Installing E-commerce tracking can require intricate knowledge of the website, particularly the shopping cart, and it is not recommended the average website owner implements it themselves unless they have the technical know-how. However, to learn more about E-commerce tracking, and see the code yourself, use this link: http://code.google.com/apis/analytics/docs/tracking/gaTrackingEcommerce.html