Making an honest mistake is acceptable. Failing to fix it is not.
If your customers are demanding, be thankful.
There are two ways to improve your service, and yourself: maximize your strengths and minimize your weaknesses.
Your promise means more than the words you use to give it.
You are the person who determines what you do. That's a big responsibility. Make the most of it.
If you want to stay in business, satisfy customers. If you want to excel in business, delight customers.