What is the ruling on purchasing a commodity with an offer that includes a gift, then concealing the gift from the customer, and what is the ruling on informing the customer of a price higher than the original cash purchase price of the commodity when selling it by installments?

If you are an agent for the buyer, you must inform him of the true price, and taking a gift is not permissible except with his knowledge. However, if you are selling the commodity, in a bargaining sale, it is not obligatory to disclose the true price. But if it is a trust sale, like Murabaha, then disclosing the true price and not cheating is obligatory. Cheating in a Murabaha sale occurs by informing the buyer of the commodity's price without informing him of an accompanying gift, because the gift is part of the sold item.

Regarding the second question, if you are an agent for the buyer or if the sale is a trust sale, you must disclose the price at which you purchased it. However, in a bargaining sale, it is not obligatory to disclose the price at which you purchased it, but cheating is not permissible. So, you either disclose the true price or remain silent about it, and it is not permissible to inform him of a price other than the true one.