Use the C.R.A.P. test to determine if the source is dependable.
Currency
Reliability
Can you trust it?
Does the author cite sources?
What is the URL suffix?
Authority
Who is the author?
Does he/she have the authority to be writing/speaking about this topic?
Purpose
Why are they publishing this?
-to sell you something?
-to convince you of something? etc.
More about the CRAP test is available from the Evaluating Information Guide.