1) Make a casino with slot machines/etc. Connect slot machines to a stock market day trading system that acts at random on each lever pull (I.E. buying and then selling 10 seconds later, when the price is a bit different)
2) Gamblers will gamble as they usually do, but since the stock market grows on average by 7% a year, they should theoretically come out ahead.
3) Casino can take 3.5% for setting everything up.
What would make this impossible?
Since that would essentially never happen on a 10-second buy/sell action on a real stock, I doubt any actual gambler would care to participate.
The issues would be
1) If you assume a 7% annual return, the return on the 10 second investment would be extremely small. 7 percent / 250 working days per year / 8 market hours per day / 60 minutes per hour / 6 ten second periods per minute = 9.7e-6 percent return every 10 seconds. On a billion dollars play through in a year you'd be looking at a $97 return.
2) I don't know what commissions are like on the volume of small, short trades you'd be doing but I imagine they would be more than $0.0000001 cents per trade which means you're losing money.
It's been a while since I used it, but API trading for laymen was somewhere between $1-2/trade at the bulk packaging.