He sells cars and refers customers to the bank, for which the bank pays him in return
Question

                I work in a car dealership. I have a deal with Islamic and non-Islamic banks. As soon as I refer customers to them for finance for the cars they buy from me they will give me five hundred dollars. Is this halaal or haraam? My second question is: is it permissible to refer a customer to a non-Islamic bank if he refuses the Islamic bank because its conditions are difficult? Is it permissible for me to sell to the non-Islamic bank which will then sell to people by its own means whatever they are?.
Praise be to Allah.
      Firstly: 

    If the bank buys a car from you then sells it to the 
    customer, and it gives you 500 dollars in return for referring the customer 
    to the bank, there is nothing wrong with that. It comes under the heading of 
    combining the brokerage and sales contracts. It does not matter that the 
    bank is non-Islamic if it is going to buy a car from you and then sell it to 
    the customer. 

    But if the role of the bank is to provide finance and pay on 
    behalf of the customer without buying a car from you, then this in fact is a 
    riba-based loan which is haraam: the bank lends the customer money so that 
    he will pay it back with something extra added. In that case it is not 
    permissible to refer the customer to the bank, and it is not permissible for 
    you to take anything from the bank, because guiding people to that which is 
    haraam is not permissible. 

    See the answer to questions no.
    113945 and
    119229. 

    Secondly: 

    It is permissible to sell the car to the riba-based bank 
    which will sell it to the customer, because legitimate transactions with 
    those who deal in riba are permissible. Hence the Sahaabah (may Allah be 
    pleased with them) dealt with the Jews, buying and selling and the like, 
    even though the Jews engage in riba. 
And Allah knows best.