Buy One, Get One Free

Q: I would like to know the following: If someone tells you to buy something for him and then to send it to him. So you go to a shop to purchase the item where it happens to be priced as: buy one (at the normal price) and get one free. In this case after buying it can you send him one of the two items and keep the free one for yourself?

A: The practice of selling one item and giving one free actually means selling two items for the price of one. When one item is sold for a price and another comes with it free of charge, the buyer is actually paying one price for two items. In fact, some shopkeepers advertise such a sale by clearly stating: “two for the price of one”; so there is in reality no "free item".

On this basis, if the first person had given you money to buy the item for him (which is probably the case in question) then it means that you had purchased both items in exchange for his money, hence both items belong to him. If you wish to keep the item, you need his permission. You may not give him one and keep the other.

Had he not given any money but merely requested you to purchase the item for him and collect the money on delivery, then you are allowed to give him one and retain the other for your own use. This is because you had now purchased both items with your own money and you are the owner of both.
In this case, delivering the item to him and collecting money in exchange for it constitutes a sale. You are selling him an item that you bought with your own money; hence you may charge him any price you wish.