What is the ruling on a shop owner organizing an offer where a customer buys a hidden item to get a 50% discount on their purchases for a week? And is this considered cooperation in sin and aggression if it prompts customers to buy what they do not need? And is it permissible for him to refuse to sell in this case?

"Rulings pertaining to the buyer's judgment intertwine with those concerning the seller's judgment; what is permissible to buy is permissible to sell under the same conditions. In some cases, the buyer's judgment differs according to their intention. If the buyer's situation could be interpreted in two ways, there is no issue in dealing with them, presuming the permissible interpretation. However, if it is certain that they are a gambler, then dealing with them should be refrained from, as it would be assisting them in sin. This is in accordance with the statement of Sheikh al-Islam Ibn Taymiyyah that intentions and beliefs are considered in transactions. Thus, every sale, lease, gift, or loan that aids in sin, if the intention becomes apparent, falls under the Almighty's saying: {And do not cooperate in sin and aggression}.

As for the mentioned competition, we do not see any prohibition in it if the hidden goods and others are sold at their market price without any increase, because the buyer is safe from gambling, as they fluctuate between gaining and not gaining, not between gaining and losing. However, an issue remains in that these promotional prizes are a gift of unknown value, and a gift of an unknown item is not valid according to the majority of scholars. Nevertheless, our preferred view is that of the Maliki school, which permits it."