Here's how "short" trades work: You sell "credit stocks" (stocks you don't actually own) to a buyer and then you buy them back at a different price. If you sell at a lower price you keep the difference. Your not in debt the money the stocks are worth, you are in debt the number of stocks. So when you buy back the stocks, your only filling the void of the stocks you didn't have. So if you sold 100 stocks at $10, your in debt 100 stocks. When you buy back the 100 stocks to vill the void, at let's say $5, then you have to pay $500 out of the original $1000 you were given, meaning you pocket $500.
Why do you need to charge money for this indicator if it's so accurate? You could be a billionaire in a week with this, why do you want people to pay you 50 dollars a month or whatever?