@AlexioP - I develop database applications on the side. One of the applications I built was for a customer who needed a customer billing system, with the usual reports.
In addition, however, she stated that sometimes she applies special credits to customer accounts, such as with special discounts, promotions, prorated statements, etc., and she wanted separate reports developed to keep track of these credits.
The database not only had to credit these amounts but also classify the credits as well. It took some time to develop the system but in the end the customer was very pleased.
Having these reports enabled her to keep better track of her credit accounting, and also gently remind her own customers about the breaks she had given them throughout the year.