There's an old story about a man who meets a boy walking along a beach. Every few feet the boy stops, picks up a Starfish, and tosses it back into the water.

"What are you doing?" he asked. "I'm saving the Starfish," the boy replied.

"But there are hundreds, maybe thousands of Starfish along this beach," said the man, "more than you could ever save. You can't possibly make a difference doing that!"

The boy stopped for a moment, then stooped to pick up another Starfish. "Well, I made a difference for that one," he said, as he tossed it back into the sea.

And so it is with your customers. In high-volume restaurants it can be tough if not impossible to save every at-risk customer. And yet, what could be a more important use of your time than to make a difference for your customers as often as you can?

Rescuing at-risk customers usually isn't all that hard, but we need to know how and where to listen.

Online review sites like Yelp, Urbanspoon (now Zomato) and TripAdviser are key listening channels. Whether we like it or not, customers use these sites and others on a daily basis to share both kudos and criticisms.

Don't take these sites seriously? You should! A University of Maryland study found that Yelp reviews could accurately predict whether a restaurant would close within the next 90 days.

Review sites are your friends, and can provide an indispensable early warning that something is amiss.

So what should you do about this? As a starting point, encourage your customers to post reviews. Not only does this give you a fairly accurate window through which to see how your guests feel about your establishment, but positive reviews can help to attract other customers.

Make a habit of checking for reviews about your business. If you see a negative review - or perhaps even a neutral one - respond to the poster and talk with them about their concerns. Don't get defensive or argumentative. Just respond with your customers' interests in mind, and do what you can to turn things around. If you can win them back you've not only saved a customer but you've shown all who read the review that their satisfaction is important to you.

Modern restaurant marketing systems come with review monitoring capabilities that will keep tabs on these sites and alert you automatically when a review is posted. This way you can focus on building your business, and never have to worry about not hearing what your customers are trying to tell you.

You simply can't afford to miss or ignore this kind of table talk. As the saying goes, "If you're not at the table, you're on the menu!"