Lets face it, a week cant go by without a technician comeback or a customer service issue. Mistakes will happen, theres no avoiding it. Obviously, you need to put systems and procedures in place to reduce the chances of mistakes occurring, but the truth is everyone at one time or another we will drop the ball.
The key thing to remember when a mistake happens is to keep the lines of communications open. With every mistake there is learning experience that everyone in the shop can benefit from.
Discuss the issue with your tech or service advisor. Get all the facts. Dont assign blame; the person who committed the mistake already knows he or she dropped the ball. Draw out of the person ways to improve and ask that person if it would ok to share the findings with the rest of the staff.
We all need to adopt the culture of continuous improvement. We can sometime learn more from mistakes then when things go smoothly.
One last note; I am not suggesting to ignore habitual mistakes or not recognize when someone refuses to improve or cannot do the job. In some cases you may have to let someone go.