Is it considered a sin for an employee to sign documents for the installment purchase of taxi vehicles with surcharges, such as insurance, color change, and collection fees, knowing about these surcharges?

It is not permissible for the bank to charge an excess amount for the value of the car, its color change, registration fees, and insurance; because in that case, it would be a usurious loan, which is forbidden. It is also not permissible to sign documents for such contracts, as it involves writing down usury, and the Messenger of Allah, peace and blessings be upon him, cursed the one who writes it. However, if the bank buys cars and sells them in installments at a deferred price higher than the cash price, then this is permissible, and there is no harm in signing its contracts.