Evaluate every source, no matter how you found it, using these guidelines:
Who is the author? Is he/she an expert on the subject, a representative from a credible organization, a columnist for a newspaper? What gives the author authority to represent that side of the controversy? (ex: US Secretary of Commerce? A lawyer? A reporter for a student newspaper?)
TIP: If there is no information on the author, try a web search on that person and the publication
Does the source (newspaper, magazine, web site) generally lean to one side of controversies (examples: liberal vs. conservative; free market economics vs. government regulated economy)?
How is the author supporting her claims? Can you find this information elsewhere to confirm its accuracy and credibility?
Are you considering the most up to date research on your topic?