What is the ruling on a seller stipulating a specific number of items per customer, especially during discount periods? Is it permissible for the customer to exceed this number, and what is the ruling on what they purchased? Does the ruling differ if the cashier or branch manager approves, or due to a large family?

It is permissible for the seller to specify the number of items purchased, and the buyer is obligated to adhere to this. The buyer is not allowed to resort to deception, because consent is a condition for the validity of a sale. Allah Almighty says: ﴿…unless it be a trade by mutual consent among you﴾, and the Prophet, peace and blessings be upon him, said: “Indeed, selling is by mutual consent,” and “The wealth of a person is not lawful [to take] except with his willing consent.”

If the branch manager agrees to sell more than the specified number, and he has the authority to do so, then there is no harm. Otherwise, it is not permissible.

If you bought more than the specified number without permission, you must consult the owner of the shop or whoever has the authority and seek their absolution. If they consent, then all is well. If they object and the item is still available, it must be returned to them. If it has been consumed, then they are not owed anything, but one must still seek their absolution.