Pro tip: You don't just hand your credit card over to a stock market.
lol I don't even know where to begin.
You cannot "hand your credit card" because stock market is not a physical entity.
Chargebacks are not only for credit card, but also for bank accounts as well. You cannot buy stock with cash, so you can request chargeback for all types of stock purchases.
Not only that, if your friend bought tons of stock with your money, you can usually sell it back almost immediately if you set the price lower than the best bid at the time. (unless it's a stuff stock that nobody wants to buy)
Ephi, don't forget that you are just a developer for an indie game. Not even, you are just a modder. Get a real job and you might see that you aren't smart and infallible.