olympus actually misunderstood me, and you were spot on :)

Brokers do charge interest rates and the rates for TESLA really were 45% (current) and 85% (once upon a time) annualized, mostly because of a deficiency in available shares. At that point it was costing 60c per share a week just to keep your short position.

Theres plenty of discussion here: http://www.teslamotorsclub.com/showthread.php/15183-Cost-to-...

Oh, wow. With numbers that high it never crossed my mind that you were talking about loan interest. Normally the interest you pay to short a stock is single digits, and if you have enough money it can be <1%.

I was thinking of this: http://www.investopedia.com/terms/s/shortinterest.asp

You can see the short interest in TSLA here published twice a month: http://www.nasdaq.com/symbol/tsla/short-interest which is very high compared to AAPL's short interest: http://www.nasdaq.com/symbol/aapl/short-interest which hovers around one day to cover.