Legitimate problems in margin trading (forex) a comparative jurisprudential study

Praise be to God, Lord of the worlds, and prayers and peace be upon the most honorable messengers, our master Muhammad and all his family and companions, and after...
The basic principle in sales is that both the price and the appraiser are delivered when contracting (the spot sale), or the price is delivered and the appraiser is postponed (the salam), or the appraiser is delivered and the price is postponed (the deferred sale), or the appraiser is delivered and the price is paid in installments (the installment sale).
But: in this research, we find a completely different picture of that, which appeared in the stock market, where the buyer (the investor) requests a brokerage firm to buy him a number of securities (shares, bonds - or commodities) using the marginal purchase system. Where he pays a certain percentage of the price, and the brokerage company (brokerage) pays the rest of the price for these securities, in return for the brokerage commission, and interest on the amount lent to the buyer. To dispose of the securities in their interest without referring to the buyer, if necessary.
The seller gets the full price of the securities, and the buyer is able to buy securities with multiple times what he has of money, and the brokerage company receives the commission and interest on the loan it provides to the buyer, and this transaction is known as margin trading.