Is it permissible to sell a product—with the customer paying 30% as a down payment—before it is manufactured, knowing that the goods were not ready with the seller or with the manufacturer?

The described scenario is closer to parallel Istisna' (manufacturing contract), which is permissible in Sharia. Its form is that the buyer agrees with a first party to manufacture goods with specific characteristics and pays the price. Then, the first party enters into an Istisna' contract with another company that can manufacture the same goods under the same conditions and at a lower price.