Is it permissible for a relative who works in his father's factory and receives a commission for car repairs to take the difference between the actual cost and the amount paid by the customer? Is it permissible if the car owner is unaware, or if he inflates the invoice amounts to take a percentage, claiming the car owner is stingy? Is this money considered unlawful?

The questioner states that he works with his father for a fixed monthly salary and is sometimes assigned other tasks for an agreed-upon commission, which is permissible. However, according to most scholars, it is not permissible for his wages for working in the factory to be a salary plus a percentage of the car repair cost.

As for inflating invoices to take the difference, or repairing a car for a lower amount and taking the remainder as a commission, this is consuming wealth unlawfully and is forbidden, because the worker is an agent. He must spend the money as he was given it, and whatever remains belongs to the employer. He has no right to take anything without the employer's permission. He must repent and return what he took to its owner. A low salary or the employer's stinginess do not justify this for him. However, if the employer gives him an amount and tells him to repair the car with it for a certain price, and the remainder is for him, then there is no objection.