Who wrote this and what are their qualifications?
Where is the information provided coming from?
How does this information compare to expert consensus?
It's important for all of these factors to taken together, and no one aspect can trump the others. Someone does not need to be an expert if they're citing research and deferring to experts. Being an expert does not preclude the need for someone to cite research where applicable. Beyond these basic vetting procedures, there are also red flags to be wary of when reviewing information online. These red flags often occur together, but even just one or two should prompt further investigation.