While I'm not an attorney, I believe a suit could be brought for monetary damages if a review like that were proven untrue, the writer knew it wasn't true, and it established a loss in brand or current sales. Of course proving someone's subjective opinion was knowingly wrong isn't easy.
And while we're on the subject, what about all the consumer reviews in Blogs YELP and other on-line consumer sites? Has anyone been sued for saying bad things about a wine in the Wild West of the Web? And a related question: What should you do about those types of reviews?