You only pay the fee if you end up paying, which is exactly the times that you make a profit since the value went down (making the coins worth less, and so a hi

You only pay the fee if you end up paying, which is exactly the times that you make a profit since the value went down (making the coins worth less, and so a higher guaranteed price is helpful to you). If the value goes up or stays the same (or drops by less than the fee) you don't do anything. You'd also need to be shorting bitcoin at the same time and covering the short at the same time as sending the transaction, but that's not hard. (Or already have the money in an account and buy it on demand, but that will add a delay) So you make money or don't do anything, stripe/coinbase is never paid for their risk.