this is very complicated, if someone doenst like your site and build negatif link to your site then your site will losing position. It is easy now to get down your competitor. I had 2 website rank on page 1 for 2 years and then i get disaster backlink pointing to my site. Someone copying my homepage on their blog/site and link back to my site and my site ranking falling badly.
Google has made terrible algorithm, blind and doesnt know who is copying and who had original content and doesnt have respect at all to original content maker
here is some link about that
http://www.seroundtable.com/...r-ranking-17150.html
the copy content rank higher that yours because google algorithm penalize your site. Funny google