Who is the author?
What else did he write about?
What kind of opinion about this subject does he or she usually have?
What is the author's connection to this specific topic?
What is the tone of the piece that was written?
Is the author consistent in his or her opinions?
When the theme is quite the opposite of this one, is the author's writing any different?
Is this source known for having a biased opinion?
Who considers this source trustworthy and who doesn't?