Is the commission paid by banks - including non-Islamic banks - for selling cars through them, permissible or impermissible, bearing in mind that the customer chooses the bank?

What banks do, selling cars without owning them, is not permissible according to Sharia. Therefore, it is not permissible for showrooms to cooperate with them in these forbidden contracts, nor to take commission from them. However, if the commission is from Islamic banks that adhere to Sharia regulations in selling cars, then it is permissible for the showroom to take the commission.