What I tell students is CHECK THE PROVENANCE. Anyone can have a web page and post any rubbish (see my posts to Mudcat for instance!). Just as you'd rely on a standard text by an expert in the field rather than a story in a shock tabloid newspaper. Look for websites with respectable origins, academic or whatever. If commercial ones, do they have an axe to grind? Would you believe a company annual report or an independent observer?
The example I use is: The typical web site owner is a male US high school student. He may call his website "The world's greatest science fiction collection" but he may only have six Isaac Asimov paperbacks on a shelf, there's nothing to stp him making that claim. The University of Texas may have a Science Fiction Collection of over 100,000 volumes. Which do you use as your source.
Sorry to go on, come to my session next Wednesday afternoon in the Library PC suite to hear it all over again!
RtS (old fart pretending to understand new technology)