With so much energy being expended on technologies that supposedly help us decide which blogs have credibility, perhaps its time to air the blogosphere's dirty little secret. The fact is that the whole notion of authority and credibility rating is based on the mistaken notion that there is some objective standard of truth that can be achieved in the social world. Come on folks the clue is in the title - social media and networking- we are not dealing with natural science here no matter how far the The technological determinists try to push us in that direction. We have to take responsibility for determining the credibility of the stuff we read. There is no independent arbiter.
Humans make use of a range of social techniques for sussing the veracity of other people. Face to face means we can check body language, listen to the tone of voice, see who hangs around with who and so on. On-line its trickier. Word of Mouth is one way to make a judgement. The initial encounter for someone is always a risk though. The blogosphere is an 'advice rich'/'repercussion poor' environment in many respects. Unless your business or profession depends on it and you need to protect your reputation you can say most anything you want regardless of how true it might be.
Perhaps the biggest error of judgement in using opinion and information on the Internet is to assume that it is somehow 'separate' from other forms of social interaction and knowledge gathering. It is simply an additional dimension to the ways that humans have evolved their social judgement. All texts are 'testimony' all texts are the voice of the author. Despite claims of objectivity every single piece of writing is governed by prior beliefs and therefore biased.
The credibility of a blog is a form of reaching for a consensus about its truthfulness. That's why SEO and the other alogrithmic ways of 'counting' authority are inherently flawed as indicators of credibility because they are a technical solution to the social problem of authenticity. Just because many people read a blog, link to a blog, comment on a blog it can in no way whatsoever be taken as an indication of the veracity of the content. Example? This post. I imagine circa 50 people will read it per day. Not the big league by any stretch. The number however can shed no light whatsoever on the credibility of the content - high or low.