(1) In certain cases, the economic replenishment interval and order quantity decrease under the permissible delay in payment, which contradicts to Goyal’s (1985) conclusion. (2) If a supplier wants to reduce his/her large level of inventory, then he/she should charge an excessive interest rate on his/her customer’s outstanding amount after the credit term expires. As a matter of fact, Teng (2002) indicates that their two managerial phenomena have been demonstrated in the decision making of using credit card. Consequently, Teng’s inventory model is interesting and is cited very often. However, Teng (2002) at least has the following shortcoming as follows: