The Dalai Lama often speaks of overcome our selfishness. One lesson he teaches is to watch our actions as an impartial observer. This is hard to do but, with practice, can yield some really good information about ourselves. This lesson can also be applied to customer service.
Next time you are at work, try to observe your customer interaction from the outside, as an impartial observer, or better yet, the customer. Ask yourself -- are you giving the kind of service you want to receive?