In marriage and customer service, I believe there has to be give and take on both sides. If one person is in the wrong, that person needs to just admit to being wrong. The customer you brought up is a good example. That person should have just said, "oh I dropped it, so maybe I should pay for the extra protection." The opposite would be true if they bought a case, the representative put it on poorly, and it broke when dropped. In my marriage, I admit when I'm wrong and my wife does the same, so we gain a stronger bond by understanding that sometimes we are wrong and we don't need to rub it in the other person's face, although in order to have a good working relationship (marriage, customer/worker, etc.), people need to admit when they mess up so the problem can be resolved without pointing fingers and blaming something else unnecessarily.
TL;DR: don't be a dick and life will be better.
What's a swife?
That's like saying the customer is always right.
@Drunken Irish Dad, try working in a cellphone store where you witness a customer drop their phone right after they purchased it with no case and no screen protector, just so they can come back in to tell you the phone was defective and it broke as soon as they plugged in their car charger.
@nuno714, apparently I forgot to hit reply, so please see my response that isn't tagged.