Is it permissible for the buyer to demand the one thousand Saudi Riyals paid, or its equivalent in goods, after agreeing with the seller to waive the paid amount and not be obligated to purchase?

The asker does not have the right to demand the thousand [dirhams] or its equivalent in goods, because a sale is a binding contract. The seller's acceptance of rescission in exchange for money is permissible, even according to the view that rescission is a dissolution and requires the return of the entire price. In this case, the buyer has waived his right to the portion of the price that was paid, and what is waived does not return. Otherwise, the seller has the right to obligate the buyer to take the merchandise and demand the rest of the price.