Is it obligatory to return the amount exceeding the value of the property, which was paid after the seller gave the buyer the choice between paying the increase or rescinding the sale, and then the buyer demanded its refund?

When a sales contract is concluded between the seller and the buyer, it becomes a binding contract for both parties. The seller does not have the right to revoke it except through mutual annulment (iqālah) with the buyer's consent. If the seller coerces the buyer into accepting an increase in price, this increase is not permissible for him, and he must return it to the buyer.