It’s frustrating to get a bad review, but it happens to most authors sooner or later.
My advice for authors is to try not to take it personally and to remember that books (especially fiction) are subjective – some people will love your book and others won’t. And many book buyers realize that most books will have some negative reviews, even if most of them are positive.
If a review contains factual errors (for instance stating that a nonfiction book was missing important information) you can click the “comment” button on the review and leave a note. But be very careful not to sound defensive – just state the facts. (e.g. Perhaps you missed chapter 6 where I discussed that topic in detail.)
If you think a review was really unjustified, you can also click the “no” button next to “Was this review helpful to you?”
If a review violates Amazon’s terms you can ask Amazon to remove it. Amazon will not remove a review simply because it’s unfavorable or you think it’s unfair, but they sometimes remove reviews that are reported for violating their terms.
Also focus on getting more good reviews to offset the bad ones.
And finally, take an objective look at negative reviews and see if there are any legitimate comments that you might use to improve your writing.
For in-depth advice on getting book reviews and profiting from them, see How to Get You Book Reviewed, available in paperback, Kindle, Nook, and PDF format.