Google is using ResellerRatings.com ratings in their Shopping section. The reviews can be done manually though the site, or through an exit survey at the end of the purchase cycle. The latter is a simple js insert in the confirmstatus control.

How to:

In BuyNow settings - Allow us to check a box if we want to use it, and a textbox for our seller ID.

And this to the ConfirmStatus ascx (or add it in code behind):

<link rel="stylesheet" href="https://www.resellerratings.com/images/js/dhtml_survey.css" type="text/css" />

In ConfirmStatus codebehind, RegisterClientScriptBlock the js.

seller_id = xxxxxx
datenow = 1;
document.write('<'+ 'script type="text/javascript" src="https://www.resellerratings.com/images/js/popup_include.js"><\/script>');