If the buyer does not know the price of the commodity or is unmindful of it at the time of the transaction and buys it for a price that is higher than its normal price, then in the event that he buys it for a significantly inflated price, he can annul the transaction. Of course, this is on condition that he is still being cheated at the time of annulling the transaction; otherwise, the right to annul is problematic [i.e. based on obligatory precaution, he does not have the right to annul].
Similarly, if the seller does not know the commodity’s price or is unmindful of it at the time of the transaction and sells it for a price that is lower than its normal price, then, in case he sells it for a significantly deflated price, he can annul the transaction on the same condition mentioned previously.