What you need to use is comments API. I have a sample for news items based on the last code snippet provided in the following documentation article. The approach for products is just the same.
You can find more information about the threadKey that you have use as parameter for GetThread method directly from sf_cs_threads table.
NewsManager manager = NewsManager.GetManager();
var newsItem = manager.GetNewsItems().Where(t => t.Title ==
&& t.Status == ContentLifecycleStatus.Live).FirstOrDefault();
// Gets an instance of the comments service
var cs = SystemManager.GetCommentsService();
//instantiate comment filter
var commentFilter =
//add filter by News
//get the comment with the specified commentKey
var comments = cs.GetComments(commentFilter);
var ratings = cs.GetThread(newsItem.Id +
+ CultureInfo.CurrentCulture.Name.ToString() +
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Sitefinity CMS Ideas&Feedback Portal
and vote to affect the priority of the items