It happens to us all. For one reason or another the customer just doesn't buy a needed service. Sometimes it doesn't matter what we could have done to change their mind, the customer was just not going to buy our suggestion.
In other cases, maybe we did make a mistake. Maybe we rushed too fast into the estimate and asking for approval, instead of explaining why the services were needed and how they would benefit the customer. Losing a sale that way can be painful. It might be helpful to magnify the pain a bit to learn from it by figuring out how much it cost you in lost commission or bonus money.
Let's say a customer needs a 30,000-mile maintenance that your shop sells for $465 and your commission would have been about $30. You just made a $30 mistake. Now take a moment to think what you can do differently so it doesn't happen all the time. By learning from the loss, you'll learn a valuable lesson about how to handle this particular transaction and how to turn all losses into gains.