No matter how great your product or service, it's inevitable that a dissatisfied customer will come your way. The key is to deal with them quickly and effectively. If you can empathize with the source of their frustration and calmly explain the problem, even if they're being aggressive or abrasive, their anger should dissipate. It's also helpful to keep in mind that they're not mad at you; they're frustrated with your business and want to resolve the situation.
Start the conversation by apologizing, even if you don't think it's warranted. It shows you care and are willing to go above and beyond for the customer. Use the customer's name when talking to them, and try to make them feel like their complaint matters. This can go a long way toward turning an angry customer into your most vocal advocate.
Often times, unhappy customers can reveal hidden problems in your business. Taking detailed notes when dealing with complaints can help you figure out what needs to be improved or reworked in order to meet customer expectations. The old saying "where there's smoke, there's fire" is very true when it comes to complaints.
Some customers are just ornery by nature. These people zap your time, energy and resources by making demands and refusing to accept alternatives that would be a better fit for their needs. This type of customer is difficult to please, and it's essential that you respect their feelings and treat them with the same level of courtesy as all other customers.