If you find your customers angry then simply dont argue with them and sikently listen to them.Dont interrupt while they are shouting but behave towards them as if you are listening to them. Once,they finished their complaint simply offer them a seat in a polite way and make them feel that you are finding the solution for their problem.If its under your hand then its good, otherwise, do call the store manager to have a solution for it and for calling a SM you must send any other staff and you must be with that customer to make him feel that what he is saying is correct. The best way to handle the customer is to agree with the words he is saying.....!!!