The questions I ask myself are
1. Is it on wikipedia? Obviously if it is don't take the advice
2. Who is the source written by? A doctor or someone who just googled symptoms?
3. When was it written? Medicine is always changing so the data could be out of date.
4. Is it from a .net .com .org .edu? Some are more reliable than others. You wouldn't want to listen to a . com as much as a .org because organizations are better than a community.
5. Does it make sense? Can you go to a doctor and not sound silly?