The first thing to look at is where did you read the story. A story on the BBC is obviously more likely to be credible than one you read on Yahoo Answers or a personal blog. If you have never heard of the outlet and know nothing about their credibility, you better check it out before you believe what they post.
For example, some of you may be coming to Wizzley for the first time. What do you know about us? Well, for one, there is a team of real life people overseeing the work of the authors. Authors go through a process of approval before first articles can be published. There is also a real set of author rules.
Compare that to Wikipedia. No initial oversight of published articles or authors. Only safeguards are a group of random people that have no vetting who scream more loudly than the others for editing. Some checks have error rates as high as 60% on Wikipedia, and yet, because it looks like a fancy site and people do not take the time to research on their own Wikipedia is used as a factual source by many.
No one site is perfect but know about the rules and regulations of the site before blindly trusting something published there. A random personal blog would need more vetting than something like About.com where the authors actually go through an interview process and are answerable to a home office.