What is the ruling of Islamic law on increasing the price of car spare parts for a customer without his knowledge, with the aim of giving this increase to the mechanic who brought the customer, and is this considered consuming the customer's money unjustly?

The answer concerning the ruling on a mechanic taking money from a merchant in exchange for bringing customers, and the merchant increasing the price of the commodity to cover the broker's fee, is divided into two issues:

1. The ruling on the mechanic taking money from the merchant: There is no objection to it, as it is a permissible type of brokerage. It is stipulated that the broker's fee must be known when there is a contract of hire (ijarah) or a contract of reward (ju'alah). However, if there is no contract, and market custom dictates a specific fee, then there is no harm in working without specifying a known fee.

2. The merchant increasing the price to pay the broker's fee: If the sale is based on mutual consent between the seller and the buyer without deception, and the buyer is not an unsuspecting person (ignorant of the value of the sold item), then there is no objection to it. However, if the buyer is an unsuspecting person, then the seller is not permitted to excessively exploit them (ghabn fāḥish); otherwise, the buyer would have the option to annul the sale or uphold it.