Share your insights or perspective on the financial matter presented in the input.

Is there any flaw in this investment scheme?
You didn't win in case B. Borrowing shares and then selling them is known as "selling short".  You received $2000 when you sold short 100 shares at $20.  You spent $1000 to buy them back at $10, so you come out $1000 ahead on that deal.  But at the same time, the 100 shares you already owned have declined in value from $20 to $10, so you are down $1000 on that deal.  So you've simply broken even, and you are still out the interest and transaction fees. In effect, a short sale allows you to sell shares you don't own.  But if you do already own them, then the effect is the same as if you just sold your own shares.  This makes it easier to see that this is just a complicated and expensive way of accomplishing nothing at all.