or the buyer, or both of them. Can it be unknown to both parties?

The answer is: Yes. This merchandise may have been imported with its price written on it by the responsible authorities, while neither the seller nor the buyer knows it.

Can it be known to the seller but unknown to the buyer?

The answer is: Yes.

Can it be known to the buyer but unknown to the seller? Yes. Therefore, it must be known. Thus, if he sells it at its marked price, the sale is invalid. This is the madhhab.

The second view is that a sale at the marked price is valid if the price has been set by the state. Indeed, this may provide even greater assurance for both seller and buyer. However, if the seller himself places whatever price he wishes on his merchandise, then the price must be known.

For example, a person prices watches and attaches a small label to a watch stating that its price is five hundred riyals. The buyer asks, “For how much are you selling it?” and he replies, “At its marked price.” This is invalid, because the seller may have marked it at many times its actual value. But if we know that the price has been determined and marked by a responsible authority, then there is no doubt that a sale at the marked price is permissible.

If, when the buyer asks, “What is the price?” the seller replies, “At its marked price,” and the buyer looks at it and finds that the marked price is excessive, so he refuses to buy it at that price, this is permissible. But if he looks at its marked price and finds it suitable, then says, “I accept,” the sale is valid, because the price has now become known.