A customer I had left their credit card behind after making a purchase and I took the time to call the credit card company, get the customer's home phone number and called them to let them know I had the card and would lock it up for them until they retrieved it. They hadn't even realized they had lost the card until they got home and heard my message. Needless to say they were happy to get that card back.
Good customer service to me is that when the person knows what they are talking about and tries not to lie to you just to sell you an item. Or another reason would be if they actually seem focused on what you are saying and how you explain things.
To me a good example of customer service is showing patience when a customer asks questions about services or products, etc. Also doing the best you can to make sure a customer is satisfied with the help you've given?