The importance of maintaining customers
If you maintain customers, then you will get good profits from being polite/correct attitude towards customers. Therefore you keep the business going, and with a good reputation which should make other customers tell other people to go their.
If you don't maintain customers, it can lead to money being lost. Say if you made food for over 200 people one day, but you lost 150 of those customers. Then you would waste food and wouldn't be gaining profits, you would be losing money rapidly a day due to the fact you was expecting over 200 people that day as usual. A bad customer service usually causes this.