What is the best way the calm down angry customer? 1 smile and listening 2 react and take action to solve problem 3 refund

i would say 1 Listen , Listen Listen 2 Agree that he is right about what upsets him/her 3 discuss solution and if it docent helps then 4 make and offer to change the experience and make it up to the customer 

Lose the smile and do other things that were mentioned especially the listening part and resolution part. Although a refund is your last resort, if the customer cannot be pacified, might as well do it.