Are commissions paid to salesmen and bank employees in car sale and installment transactions permissible or forbidden, especially if they involve increasing the car's price for the buyer without his knowledge?

An employee is not permitted to take a commission from clients unless authorized by their employer. This applies to any commission paid to them as long as they are performing their obligated work for which they receive a salary. The transaction for which the commission is paid must be permissible by Islamic law. Thus, it is not permissible to take a commission on usurious loans. Nor is it permissible for an employee to inflate the price of a product to take the difference for themselves or share it with another employee. This falls under unjustly devouring wealth, which Allah has forbidden, saying: "And do not consume your properties among yourselves by unlawful means." Unlawful means include lying, cheating, forgery, and bribery. The lawful alternative is for the one entitled to the commission to stipulate a commission from the seller or buyer that they will take from them.