Obsolescence management

Hi guys! Can anyone has an idea on how to manage this type of situation? There is an agreement between Company ABC with on of its customer where comapany ABC agrees to reclaim products that the customer doesnt want to keep anymore. In consideration of that, Customer ABC grants a discount to the customer which the maximum amount is agrees with all parties. The discount cannot exced a predetermined amount. That discount is given to the customer as credit of 5% of all subsequent purchase invoices until a total amount of the discount registered in the agreement. The credit amount is calculated on the total amount of the invoice minus all taxes and freight charges. The balance of the discount is printed on the invoice and on the account statement. Thanks for anay idea or suggestion.