Good and Bad
The customer service is there to help and assure that the customers are happy with what they have got from the store and to make sure they know, that if there is any problems with the products bring it back and let them know. That should result in getting a new one or a refund.
Bad customer service
Bad customer service is not only bad for the customers but for the shop as well.
People will give it a bad name and people will stop coming in because of your reputation, this will affect everyone down the line including the supplier etc.