What is the ruling on writing the original price in an invoice for car spare parts, given that there is a discount and the amount has been adjusted, based on the customer's request because the merchandise is not for him?

If the sale involves deceit, falsehood, and treachery, then it is not permissible. It is also forbidden to issue an invoice for more than the amount paid, so that the buyer can receive a [refund or compensation] in return; because that is deceit, falsehood, and treachery, and it is not permissible.