According to an article recently published by Review Trackers, a company devoted to improving reputation management and customer experience, 94% of consumers avoid a business based on negative reviews. The same source states that 45% of consumers are more likely to visit a company that responds to negative reviews. Therefore, responding to online reviews written by customers is an increasing responsibility of customer service.
Answering customers' reviews is a sign of respect for those who took their time to improve the quality of your product or service, and it's also an opportunity for customer service teams to offer their side of the story and reduce possible brand reputation damage. It also shows readers that you're willing to get better and provide a good and reliable service, although you might have made a mistake.