Deciding if a source is authoritative enough to base your research on is easier than you think. Just consider these 5 criteria. For details, check out out tutorial on Evaluating Resources
Currency: When was the information published or updated? Is there more recent information available on your topic?
Relevance Who is the intended audience? How in-depth is the information? Is the information overly basic or highly specialized? Is the information appropriate for your research?
Authority Can you find information about the author from sources? Is the author a self-proclaimed expert or enthusiast? What are the author's or publisher's credentials?
Accuracy Is the information well written? Is the information verifiable elsewhere? Are the sources of information documented?
Purpose Is the information biased or prejudiced? Is the information designed to entertain, disseminate scholarly information, or sell something? Is the information presented complete? For internet sources, how is the site funded?