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Shorting: What if you can't find lenders?
If you can't find anyone to lend you the shares, then you can't short. You can attempt to raise the interest rate at which you will borrow at, in order to entice others to lend you their shares. In practice, broadcasting this information is pretty convoluted. If there aren't any stocks for you to buy back, then you have to buy back at a higher price. As in, place a limit buy order higher and higher until someone decides to sell to you. This affects your profit. Regarding the public ledger: This functions different in different markets. United States stock markets have an evolving body of regulations to alleviate the exact concerns you detailed, but Canada's or Dubai's stock markets would have different provisions. You make the assumption that it is an efficient process, but it is not and it is indeed ripe for abuse. In US stocks, the public ledger has a 3 business day delay between showing change of ownership. Many times brokers and clearing firms and other market participants allow a customer to go short with fake shares, with the idea that they will find real shares within the 3 business day time period to cover the position. During the time period that there is no real shares hitting the market, this is called a "naked short". The only legal system that attempts to deter this practice is the "fail to deliver" (FTD) list. If someone fails to deliver, that means there is a short position active with fake shares for which no real shares have been borrowed against. Too many FTD's allow for a short selling restriction to be placed, meaning nobody else can be short, and existing short sellers may be forced to cover.