How to Evaluate the Credibility of a Source (excerpted):
1. Think about how reliable you need the information to be. Everyone has different standards for credibility, and often this depends on how the information is going to be applied. If you're writing an academic paper in a university setting, for example, you need to be especially strict about sources.Articles like these will never go out of date, they will be rewritten for the current level of technology. This is the spiritual heir to Aristotle's The Poetics.
2. Consider the medium with which you are working. Generally, the more that is invested into the creation and publishing of the material, the more likely you are to find reliable information. For example, printed material has a higher cost of production than an Internet blog, which anyone can publish for free....Take everything with a grain of salt.
3. Research the author.
4. Check the date.
5. Investigate the publisher.
6. Determine the intended audience.
Tips: The more radical the ideas presented in the source (in comparison to other sources on the same subject) the more carefully you should scrutinize it.