If you run a restaurant, it is inevitable that you might get a negative review at one point in time. When that happens, it should not cause you unnecessary panic. You should first start to understand the genesis of that review by reaching out to that customer if it is possible. The important thing is for you to approach the situation in a diplomatic way.
Managing the Crisis
Be calm as possible when you see a negative review about the restaurant. Do not make an apology that sounds
as if you are trading blame 
to the person who has complained. Instead, you should own up if your restaurant is at fault. The next step is to seek if there are ways you can make up. For instance, if a customer is complaining of being overcharged, you should find ways of offering a refund. Resist the urge to get into an unnecessary exchange with the customer, as it will come off as extremely unprofessional. If the review is public, assure the public that it has been worked on and resolved so that they know that you have made the needed changes.