Not responding to a customer's complaint on Twitter is like hanging up the phone on him--with millions watching.

No matter the size of your business, your success will always lie in your ability to deal with customers. In an age when consumers have so many different options they can turn to, one factor that can significantly set you apart is effective, reliable customer service. I've written about how to deal with customer complaints on the phone. But what about online complaints, which are public and can quickly spiral out of control thanks to social media? If you can effectively handle a customer's online complaints with hundreds, thousands, or even millions potentially watching, it isn't just customer service, it's also marketing.

To handle online complaints successfully, simply follow two rules, each with its own abbreviation: DND (do not delete) and LAST (listen, apologize, solve, thank).

Do not delete (DND)

Do not delete any online complaints about you, no matter how tempting that might be. The only exceptions to this rule are obscenities, profanities, bigotry, and posts that call out employees' private information. If you delete a complaint on your blog or Facebook page or elsewhere, that's the opposite of good customer service. That's telling the customer that he or she doesn't matter, and it's inviting him or her to find another forum and get louder somewhere else. (If you don't believe me, check out the United Breaks Guitars video on YouTube.)

Instead of deleting complaints, here's what you do:

Listen, apologize, solve, thank (LAST)

1.  Listen

Use the social Web to listen for complaints made directly to you and indirectly about you. Search your company name on Twitter, and actively review your Facebook page and blog and any forums in your industry. Pay attention to every site online where people might be talking about you, so you can find each and every complaint and make sure none of them go ignored.

2. Apologize

Here is your chance for the company to shine. Look at the complaint as a gift, a moment to show off how responsive you are and how much you care about your customers. Everyone makes mistakes. Customers understand that. They just want you to fix it when you screw up. It really doesn't matter who's right or wrong; it matters how your customer feels. So say, "I'm sorry" (which is much more personal and better than "I apologize" or "Our apologies"), validate the customer, and vow to resolve the issue privately. This de-escalates the issue while still telling your customer (and anyone else watching) that you care.

For example, if John posts a complaint on your blog or Facebook page, you can respond, "I'm so sorry you've had a bad experience, John. That must feel awful. We've sent you a private message to help resolve this."

3. Solve the problem

It's important to say "I'm sorry," but unless you can solve the problem, it won't matter. Make sure you have a customer-centric organization that can resolve the problem, no matter what. Give the customer her money back. Give her a free month or two. Surprise and delight her with something awesome. No matter what, make sure you can leave the customer satisfied or, better yet, thrilled.

4.  Thank the customer

Remember, the complaint really is a gift. It's an opportunity to fix a problem, learn how to improve, and show the world watching how much you care about your customers. So genuinely thank your customer for hanging in there with you. This will make him or her feel heard and assure that despite the initial cause for complaint, you're optimizing your chances of keeping him or her a customer for a long time to come. 

When you follow these simple rules, you can turn an angry customer into a fan for life. More important, you can turn a potential online reputation issue into a marketing opportunity. Comments on the Internet--the good, the bad, and the ugly--last forever. So do your responses.

How do you deal with customer complaints online?