This topic just get hot recently

After several Chinese exchanges opened the option to do leveraged trading, many doubted that they can essentially create many bitcoins out of thin air based on fractional reserve principal, then they could use those coins to short the market and squeeze out many traders to get real coins in their hand

Of course, they can also create fictional fiat money to push up the price by many folds using the same practice, most possibly MTGOX has already done that and that is the main reason the exchange rate fluctuated so dramatically before

So what is your opinion about this? Even if you auditing an exchange and make sure their cold storage contains 50K coins, it does not stop them from creating 500K coins sell pressure using a fractional reserve ratio of 10%