Customers can always find something to complain about, whether it be a tiny snag in a sweater or that you didn't greet them correctly when you arrived at the store. As you know, there's no need to blame the customer. It's up to you to respond most politely and kindly possible. Their frustration could be from their recent breakup, or maybe they're just having a bad day. Your job is to tell them, "I'm so sorry that happened! What can I do to help?" A can-do attitude will take you far with customers, especially when you can solve their problems.