An angry customer can make you angry, too. however, it is crucial that

When dealing with a customer that is upset, instead of getting easily frustrated or angry it is crucial that you breathe, remain calm, and ask the customer to explain to you what is upsetting them, or what has gone wrong that has caused their anger. Do not interject while the customer is speaking. This will allow the customer to blow off some proverbial steam and give you the opportunity to fix the problem.