If your car is on bank loan, you have two choices, tell the buyer to take over the loan as is if he's willing OR tell him to pay you the cash, more or less, so that you can close the loan and transfer the car to his name.

If he gives you cash you have to go and settle off the bank loan first before you can transfer the car. You could also try going to these car dealers on salwa road and strike a deal with them, they normally will take a percentage of the sale.

Try qatarsale.com as a more reliable source to sell cars.