Is it permissible to conduct a transaction involving the sale of goods in installments through a loan company that intervenes in the sale and charges a file preparation fee of 150 dirhams, knowing that the selling price does not change whether the payment is made in one lump sum or in installments over 10 months?

It is permissible to purchase goods with cash without any issue. If the buyer pays the price of the goods to a loan company in installments without usurious interest, there is no harm in that, and the expenses paid do not affect the ruling if they are actual service fees. The resolution of the Islamic Fiqh Academy states that fixed fees for services are not considered usurious interest, and any increase beyond actual services is forbidden because it is usury. A distinction can be made between usurious interest and service fees: interest varies with the amount, whereas service fees are fixed and proportionate to the service.