This is not the first of such cases, but it may have a good chance of success anyway. In 2011, a plaintiff cosmetic surgeon's case was dismissed and the surgeon ordered to pay $20k in attorneys' fees to a former patient who had posted a bad review. A computer graphics company in Florida sued a former client for defamation as well, alleging a 70% drop in business. The outcome is still pending there.
Defamation -- that is, a knowingly false statement published about someone or their business which causes damages -- can be expensive. If you experience a loss in business as a result of false bad reviews, there are steps you can take instead of or in addition to suing for money damages. The most important thing is to "stop the bleeding" and try to improve your "Search Engine Optimization" (SEO) so that the recent bad review is not the first thing that pops up when someone searches for you.
SEO can be expensive if you outsource, but it might be worth it to put the hours in yourself. The goal is to frequently update your online presence. If you don't have a website, get a free one and start blogging immediately. Comment in a positive way on other websites while using your real name. Use your online presence to promote other positive things -- maybe you volunteer at a soup kitchen, maybe you foster rescued puppies, maybe you crochet -- so that, over time, there are many positive associations with your name and your business, which may dilute one really stinky review.