Is repentance sufficient to clear one's conscience, or must the money be returned to the customer after the increase taken by the shop owner without their knowledge?

It is permissible for the owner of the commodity to sell it at the price he desires, provided there is mutual consent between the seller and the buyer, according to the Prophet's (peace be upon him) saying: "Indeed, selling is by mutual consent." There is no harm in raising the price if the buyer agrees, unless the buyer is a naive person who is not skilled in bargaining. In such a case, it is not permissible to intentionally deceive him, and he has the right to return the commodity. If the seller knows that the agent has cheated the buyer, he must repent to Allah and return the excess amount to the buyer if possible; otherwise, it is better to give it as charity.