1. Listen Positively and Empathise

Don't try to defend yourself or the company. Allow the customer to let off steam. Show understanding.

What seems to be the problem?
Can you elaborate?
Could you give me the details?
That must have been very irritating.
I understand how you must feel.

2. Admit the Mistake and Apologise

Don't put the customer on the defensive or question his judgement. Admit mistakes immediately.

I really am sorry.
It seems something has gone wrong here.
There's definitely a problem here we need to deal with.
I'm very sorry about this.
I must apologise on behalf of the company for this.

3. Accept Personal Responsibility

For customers, you are the company. They don't care whose fault it is. You have to deal with it. If the problem can be dealt with only by someone higher in the hierarchy, stay with the customer until it is clear that the problem is being resolved.

I'll make sure this is dealt with.
Let me see what I can do.

4. Act Immediately

Show customers that you are taking their complaints seriously.

I'll get on to it right away.
Let me see what we can do to help you immediately.
I'll deal with this straight away.

5. Offer Compensation (if possible)

Demonstrate your concern practically if you are able to. Often, the form of compensation is less important than the thought.

Please accept this to make up for some of the inconvenience.
Would you like a cup of coffee while you're waiting?

6. Thank the Customer

We should be grateful for complaints. It's one way we can find out how to improve our service. Remember, too, that it costs five times as much to gain a new customer as to keep an old one.

Thank you very much for bringing this to our attention.
Thank you. This will help us to improve our service in the future.