With the arrival of social media, a simple negative review is enough to find yourself in a "bad buzz" that will severely impact your brand image. Nevertheless, with a well-defined strategy, these critical situations can be, almost, fixed with no harm !
In order to react quickly to a crisis on social networks, your brand must have a Social Listening strategy in place. Tools like Talkwalker or Karma can be very useful in these kind of situations. These tools crawl the internet and social media, looking for posts where your brand is mentioned.
Your brand needs to have a clear idea of what constitutes a real crisis on social media and a predefined protocol for responding (you don't want your teams to overreact to small issues)
Your teams need to acknowledge the problem in public and make sure that customer criticism is listened to.
This doesn't mean your brand has to admit to being at fault, but to acknowledge the problem.
Ask for forgiveness from your customers whether you are at fault or not.
Most bad buzz on social networks can be avoided by clarifying a few misunderstandings caused by miscommunications.