Like I said I'm not an educated investor? They will say it's to protect the customer, but in reality they are just protecting themselves, as they are likely concerned about the scarcity of shares and their ability to actually deliver, as they almost certainly do not hold an inventory of their own, meaning they would have to buy them from somewhere, what do you mean by actually deliver? Why would the brokerage firm need to buy shares or have shares in inventory? Sorry just trying to learn here if you can break it down further
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