It is difficult to determine just what constitutes common courtesy nowadays. In some quarters, courtesy has been associated with a stuffy system that kept women out of powerful positions or with an insincere amiability that shouts, "Buyer beware!".
Setting that aside, it appears that the little courtesies such as writing thank you notes, remembering birthdays, and treating others with an extra amount of kindness are seen less frequently than in the past. I'm hardly a saint in this respect. This is a confession as much as it is an observation. But when you encounter a person from the old school, it is a reminder of how much we've missed.
I mention this because a friend recently received a thank you note from her daughter's pediatrician. She was pleased and somewhat surprised to receive it and the doctor's stock, which was already high, rose considerably as a result. Part of the note's impact was due to the fact that it was not necessary. It was an extra kindness.
We can list the business benefits that can flow from such gestures, but that may be cheapening the sentiment.
Instead of looking for a competitive advantage in courtesy, isn't it sufficient to note that it is the right thing to do?