Customer service is the biggest reason people switch brands. A happy and satisfied customer will share his experience with 5 friends but an angry customer will go on top of the hill and shout about it to 50 of his friends. The fact of life is that we all screw up. Some products end up being defective, some days aren't like how you thought they would be. How would you react when you got late for a date, or you promised your family a good vacation but circumstances led you to not fulfill it. You would say "Sorry" and try and make up for it. An unhappy customer is the result of an unfulfilled promise made by your product. You need to simply say sorry. Most customers like normal human beings will understand. They'll understand that you are genuine in your approach. And that is what matters. Your repeat sales orders would be a testimony to this approach. The subtle smile would travel till your next repeat order. They'll remember the experience, the personal touch. It is the stepping stone of building a long term relationship.