How do I get my store reviews or ratings to appear in Google Shopping?
Unfortunately, there is currently no way to control any aspect of your seller reviews or ratings in Google Shopping via data feeds.
Google provides some advice regarding seller ratings in the links below. Basically, the domain registered on the third-party review site must match the domain registered in your Google Merchant Account, and there must be at least 30 reviews. Meeting these requirements is not a guarantee that the reviews will be listed.
Changes are coming soon though. They are now accepting reviews from Bazaarvoice and PowerReviews, if you subscribe to their paid review services. Google also hopes to add additional partners, as well as a self-submission model.