Re: Rating extension
If you talking about Seller Rating extensions, it's show in the form of stars below the ads, primarily to showcase customer's experience with the merchant as opposed to a specific product. This helps online shoppers find highly rated retailers and merchants online by similar online shoppers across the globe.
Unlike most extensions, you don’t need to create this within your account. If you are eligible to show these extensions, they will automatically start to appear. To be eligible, your business must have at least 30 unique reviews -- each from the past 12 months -- and a composite rating of at least 3.5 stars or higher.
Also, you can accumulate reviews from any of these independent review websites for your store (please note that there may be costs incurred with using some of these services).