> who do you make money from?

When you own stock at a broker in a margin account, you may sign an agreement to allow the broker to lend out your stock to someone else. For lending your stock, you are entitled to a stock-borrow fee which usually is quite small say 0.25%, and paid by the borrower (short-seller). The borrower then sells the stock to someone else. At a later point, the short seller closes their position by buying it back, and returning it to you. This is roughly the mechanics of it. So, to answer your question, the short seller makes money from folks who buy high and sell low. In this specific example, the stock-borrow fee say was 5% because, the float is still low, and if the short seller borrowed at $165 after the IPO and sold it, and then bought it back at $135 and closed their position, they made money from folks who bought at $165 and sold at $135.