Arguably, the most effective way to lodge a complaint is to do it in a calm manner, and by presenting the facts and proposing a solution. But if you're on the other end of the complaint, you might encounter an irate or even angry customer at some point.
The trick here is to keep calm. Here are a few things you should remember, as well as a few steps you can take to resolve a complaint in a way that everybody wins.
Listen. The first thing to do, when faced with a complaint is to actively listen. Active listening means you give cues and body language that signifies you are actually thinking about what the other person is saying. You should also take notes of details or other information pertinent to a complaint, so you can refer to these when thinking of a solution.
If you're being met with a complaint in person, look at the complainant in the eye, and nod in understanding. If you're on the phone, don't just keep silence. Give cues, such as "Please go on," and the like. The important thing here is that you don't get into an argument and that you don't disagree, because this would only escalate the complainant's anger. Then summarize the complainant's points, to make it clear that you've understood their points, and to check if you've missed out on any.
Empathize. Acknowledge the problem of the customer, and try to determine if it is a valid complaint. First try to visualize how you would feel if you were in his or her situation. This would help you better understand the reasons behind the complaint, and perhaps even the reason behind the outburst. It's important that you let the complainant know that you would feel the same way if it were you in that same situation. This would help diffuse his or her anger, and knowing that you empathize, the customer would then better cooperate with you in looking for a solution.
Apologize. You need not take the blame personally, but it's important that you apologize on behalf of your company or business if indeed you made a mistake at some point. Or at least apologize for the inconvenience. Owning up to a mistake tells a customer that you care, and that you are willing to make amends for any mistake you may have made. If you feel that your company has not wronged the customer in any way, still try to resolve the problem in a fair manner.
Compensate for the trouble. The best companies don't only resolve a customer complaint by refunding, replacing or exchanging an item or service. It also helps with your brand or company's image if you give an additional extra, just for the trouble. It doesn't matter if it costs you money. The important thing here is that you extend goodwill, and this does wonders for your business in the long run. Not only would you be able to win back an upset customer, but you will probably regain that customer as a happy one, who would likely even recommend your business to friends because of the nice way you have treated him or her with his complaint.
In the end, the important thing is to be nice, and to extend a helping hand. Customers are the lifeline of any business, after all.