Check to see if the author and publisher are reputable. For example, is there any indication that the author is an expert in the subject presented?
Ask:
What are the author's qualifications? Is the organization publishing the information reputable?

Look at the domain of a web page: is it an education (.edu) or a government (.gov) site? These may be more credible than commercial (.com) sites or those of supporting a cause (.org). Go to "Anatomy of a URL" if you are unsure how to determine the domain of a web address.

If you can't find information on the author or organization publishing a source, you should question its reliability.