Is it permissible to purchase a product in installments from a store that adds an amount (which they call interest) to the monthly installment, knowing that the price of the item in installments will be higher than its cash price, and is it permissible to purchase it through a company owned by a Muslim individual to obtain a 30% discount, with the original buyer paying the full amount?

It is permissible to buy in installments, even if the price is higher than the cash price, provided three conditions are met: the purchase must be from the owner of the commodity, the contract must not separate the price from the increase but rather state the total price, and the contract must not stipulate interest on late payment. There is no harm in paying a portion of the price and deferring the rest.

Similarly, it is permissible to buy through a company to obtain a discount, unless it is known or highly probable that the seller restricts the discount to the company's employees. If the seller prohibits this, the company owner can buy the commodity for himself and then sell it to you at the same price, or more, or less, either in cash or in installments. This is called "Tawliyah" (resale at cost) and is permissible in Islamic law.