Is it permissible to sell a commodity by paying 20% of its price to the manufacturer, then selling it in the store and taking the profit, and then completing the payment of the remaining 80% to the manufacturer?

If you purchase a commodity from the manufacturer in a valid transaction that fulfills all its pillars and conditions, and you take possession of it, then there is no impediment to selling it. Your sale is not harmed by the fact that its price, or most of it, remains a debt upon you, due to the Prophet's (peace and blessings be upon him) saying: "If you buy a sale, do not sell it until you take possession of it."