It is essential that you evaluate every source and argument that you use. Do not take things at face value. Always question the accuracy, currency, credibility and bias of authors and sources. See the two pages here on evaluating sources, and also the resources listed below.
Evaluating Internet Research Sources from VirtualSalt. http://www.virtualsalt.com/evalu8it.htm
Critically Analyzing Information Sources from Cornell University. http://olinuris.library.cornell.edu/ref/research/skill26.htm