There are various methods for evaluating web pages. See the link at the bottom for a detailed method. Here's a brief one.
Quick Checklist (from Info-People):
Who is the author of the piece?
What institution (company, organization, government, university, etc.) or Internet provider supports this information?
When was the information created or last updated?
What appears to be the purpose for this information? Inform, Explain, Persuade.
Who is the intended audience?
Compared to what? -
What does this work/site offer compared to other works, including non-Internet works?
If you need more help evaluating websites, check out the Five Criteria for Evaluating Web Pages.