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Is there a way to tell if sites are on the same C-Block so I can get more C-Block links? You can visit the site and use the MOZbar Analyze Page > Page Attributes function to see the website's IP address. Another method is to simply ping the web address using the command prompt. IP addresses are provided in the following format: AAA.BBB.CCC.DDD. The idea behind the C-block differentiation, is that is one of many methods Google uses to determine a relationship between websites. There are numerous other methods Google or Bing can use as well.

As Zachary says, these results are personalised. The best way to check is to use incognito in Google and Private browsing in Firefox whilst being logged out of your google account. This should remove any personalisation from your searches.