As people engaging in seo should know how vital important a backlink means to the rank of a website. So, how to judge a backlink? There are four factors in general, ie Relevance, Authority, Extensity, and Healthiness. 1 Relevance As for relevance, I bet all of you know this point. Esp when exchanging links, most of the webmasters would seeking for counterparts. for exchanging We can imagine that when choosing the best doctor, the vote from a doctor or a nurse or a patient is much more persuading than a vote from a non-medical person . In the same way, the backlinks is like the votes to the websites. The more the relevant is , the more persuading the vote is. 2 Authority As for authority, we can follow the previous voting topic. In healthcare field, there are chief physician, deputy chief physician, physicians, nurses and so on. A vote from a chief physician is much more important than a nurse without doubt. By the way, you can imagine there is a mayor who doesn?t know medical industry ,yet he does not go to see doctors often. However, a vote from this mayor is even more important than many medical professions. And that explains what authority is. 3 Extensity When we say extensity, we mean the IPs of backlinks are widely distributed. By the two points mentioned above, you can reason out the answer why the IPs should be widely distributed. Let?s continue our voting topic. We all have rights to vote, just like the internet, each web can be inserted with links. In a family, there are four people. If this family all vote to the same doctor, that is four votes. Well, there are four families, one out of each family votes to the same doctor, there are four votes as well. For the same four votes in the two cases , obviously, the latter case is more important than the former one. That is what extensity of backlink is. 4 Healthiness We all hope the backlinks are healthy without illegal content. Just like Voting. I think both you and me will not admit a vote from a criminal or a liar. What?s worse, such a vote may even cause opposite effect. Of course, you don?t need to worry your competitors will insert your url into jank sites. Cos search engine will ignore such a link. But, if there are thousands of junk links, that make difference. In the end, you may think it is useless to buy bulk junk links. You can consider comprehensively , And hope this is of some use for the SEO beginners.