It is a thing that you have to keep in mind: customers are from all sort of background, with different levels of education, from various cultures. So, it is normal that they act differently. You have to treat everyone with respect and professionalism, as required.
Firstly, there are customers who come here angry. That does not mean they are angry with you. It might be an issue with the product or service they were given. Some of them could have had a bad day previously to come here. Your role is to try to calm them down, but not by asking them calm down or shouting so that to cover them. Try to be polite, to listen to their issues, smile and talk slowly. The empathy is a must, so that the customer feels you on his side. Never contradict a customer even if he has not right, but demonstrate that you are on his side and eager to help. Apologize for the inconvenient. Not blame anyone for his problem. If you could help him, help. If not, try to put him in contact with a supervisor, coworker of any other department. Before transferring him to anyone else, ask his permission first. If the matter can be solved by you, as a reimbursement, a change, do it. Try to imply the customer in this, presenting some possibly solutions and let him chose or ask him for the permission to follow the procedure. When the problem is solved, to keep the person satisfied you will give him a reward card with some per cent off on his future sale from our store. This way you have him satisfied and he will return to buy from us, since he has a coupon with rebate. In the end ask for his phone number and email address and do not forget to contact him for a brief follow-up. This way, that customer will remember you and our company for the professional way he was served, and be confident to do business with us in the future.