We've all heard that we should avoid talking about ourselves. As a general rule this is a way to avoid appearing self-centered, which is a good thing. But there is time to break this rule, and this is when it will avoid confrontations with clients and coworkers. How does this work?
In conversations, just as in physics, each action has an equal and opposite reaction. You push me I push you, you pull on one end of the rope I pull on the other. This is not what we want when we have not met a customer's expectations.
So where does the focus on self come in? It works in a positive way when you place the responsibility for the situation on yourself. Imagine you are serving food at a restaurant and as you lay out lunch for a table one diner becomes irritated with you. "I wanted tuna salad, not chicken salad," he barks. Now you know, beyond a shadow of a doubt that he said chicken. The woman with him said "I'll have that too," and is already three bites in to her sandwich with no complaints.
Remember your big goal here is to get a tip. Winning an argument won't put a dime in your pocket. So instead of saying "You said chicken, but I'll change it for you no problem," you don't push back. Don't put the responsibility on him.
Try this instead. Don't grimace or smirk. Pick the plate up and say "I'm sorry I brought you the wrong thing. I'll get this changed as quickly as possible." No arguments. You may still get a gruff comment or two, but you haven't provoked your customer any further. And you ARE sorry it was the wrong sandwich, whatever the reason. In some cases your partner in the transaction will actually realize later that they have made a mistake.
This will not always work. But arguing with clients is a losing proposition. If you've got documentation you may sometimes need to say, "I'm sorry, you did sign a contract listing 1 PM as the start of the show," but do not ever forget that your ultimate goal is to earn money. Theirs. And they won't give it to someone they resent.