Unhappy customers grab a megaphone. What we fondly call 'review rage' manifests on blogs, social media and online rating websites such as Yelp.com. TripAdvisor.com or DexKnows.com. But the happy customers hardly are motivated to leave online reviews.
The real problem is amplification of one sided tone. The only way to balance out is take control of it. Know why few of your customers had poor experience, and fix it at the source.