If a customer is angry, It's only because he is not able to resolve a particular issue. It's the issue that is frustrating him and not the agent with whom he is talking to. He wants to get rid of the issue as soon as possible. I too faced such customers, the thing they want from us is "Resolution", "Assurance that we understand his/her issue and we will fix it". We should first make the customer feel comfortable by assuring that we understand his/her issue and we do have all the resources to fix it. Our soft skills are very important in these situations. I sold new P.C.s to an irate customer too.