Barber's final test

I think that when a barber does his/her final practical exam, they get evaluated on certain aspects of the haircut. I believe that they get bonus points for this classic barber move:

The barber stops cutting your hair, apparently finished, then lifts up the hand mirror so you can see the back of your head. You nod and say something positive and they suddenly notice something they missed, something very small. They pick up the clippers or scissors and perform one last touch-up before letting you out of the chair.