When you have products in inventory, keep track of them here. As you add to your inventory provide your purchase prices and optionally other information, like expiry dates, or storage locations.
When you create a customer order that includes a product you have in inventory, you can also enter how many of the units ordered are to come from your inventory. You customer sees no difference in their invoice. Simple and easy.
When this customer order is closed the accounting of the inventory purchase is made considering the purchase price that you made for the inventory, not your usual purchasing discounts. Also any differences in sales tax paid verses collected are also calculated.
With this integrated inventory management, all your customer orders are scanned to ensure that your inventory is not oversold.
Your gross profit charts and cost charts includes the inventory sales information.
Your inventory sales information is separately summarized in the business report automatically created every time you close an order cycle.