If you face a problem with a customer in puplic the best thing to do at that point is try has calm has possible move the customer away from the puplic eye. for example you can tell the customer with not with a loud voice but stronge vouce to follow you some where away from the puplic eye, after get them away wait until they have said everything in their mind let them shout do not say a word at that time. When the customer has cold down a bit offer them a soultion to the problem they had, after give them something a little extra just to make them smile. After all that talk to the customer a bit find out in detail what went wrong, at this point the customer is much calmer and you would be able to understand them better, take notes of what they say. learn from your note how to make sure this doesnt happen again, teacher team mates.