There is no problem with the funds provided by securities companies to buyers and sellers of margin financing and securities lending. As for the securities provided to brokers, some of them are self-operated, that is, the stocks held by the self-operated business department of brokers for a long time, some of them come from the stocks lent by brokers, and of course some of them may come from the loans lent by corporate executives.
The current refinancing business refers to enterprises lending their idle shares to brokers to obtain interest income from them. Although it has not been officially opened, in fact, many enterprises have done so.
There is no such thing as over-the-counter gambling. If the securities broker does not have the corresponding number of shares, the securities lender will not be able to obtain shares. It is extremely difficult to borrow money now, and I often want to melt everything. In other words, you are not allowed to sell stocks you don't have. This is called naked short selling.