No they can put up the money to the tune of 150% of the price of the stock. So that means if they short a stock at $1.00 they have to put up $1.50. So if the stock goes to $2.00 they then have to come up with $3.00 a share which means they have to put up another $1.50 per share. and so on and so on. Which is why when some people complain about shorting a stock st a dime it doesnt make much sense. Best you can do is for the stock to be delisted in which case they have made .10 per share. But if it goes to a buck OUCH