Is it permissible to deal with a brokerage firm in the financial market that allows the purchase of shares exceeding the deposited cash balance, without interest and for a short period, while the firm charges a commission on buying and selling?

It is impermissible to deal with a brokerage firm that lends money to clients to complete the price of shares and takes a commission for that, because this benefit accruing to the lender is considered usury (riba), for every loan that draws a benefit is usury. However, if the broker lends money to people for help and assistance and takes a commission for the services he provides, and his situation does not differ between the borrower and others, then there is no harm in dealing with him at that time. A condition for the permissibility of buying shares is that those shares must not be in companies that deal with usury, or deposit their money in usurious banks, or trade in what Allah has forbidden.