In implementing dynamics NAV, I often go through explaining supply and demand. Companies which trade products often do so by managing the supply and demand parameters outside the ERP system. Often the ERP system does not support real planning tools and therefore the staff is forced to come up with alternative ways. In those cases, I would go as far as saying the system is not an ERP system. It is more like an order and invoice printing system. In my opinion Quick books falls into that category.