The greatest customer service lessons come from customers themselves. One of my favorites is a customer who said to me, "Sometimes you have to bend a few rules to make it happen."
I had just given him a laundry list of reasons why I couldn't get his order produced and shipped by the time he wanted it. He and I both knew it was a one day job that was going to take two weeks because of my company's rigid policies and inefficient processes. My customer's comment stopped me in my tracks and made me realize I didn't add any value to the relationship if I couldn't help my customer achieve his goals.
Needless to say, I bent a few rules to make sure the customer was happy and didn't take his business elsewhere. It's a good lesson for all of us: bend (but don't break) the rules when it's necessary to do the right thing and save your customer's business.