When an author receives a negative review, usually the first thing they feel is disappointment that the reviewer didn't like the book the author worked so hard on.
If said author is a professional, the only reaction (if any) they should show to the world is a polite and matter-of-fact "thank you" for the review, no matter how much they are angered or insulted by what was said.
Or alternatively, they might respond as this one did.
http://booksandpals.blogspot.com/2011/03/greek-seaman-jacqueline-howett.html
Agent or not, contract with a big publishing house or not, professionalism is still professionalism, and it is absolutely paramount if you want to get anywhere as a writer.
