MetroCard had so many scams.

The easiest was just to hang out at a busy station. Plenty of people would throw their card on the floor after entering. There was a machine at the token booth that told you how much was left on the card. Enough people would just toss cards with low balances that homeless folks would be there scavenging them.

They used to sell an unlimited rides for one day card. People would buy four or five and offer entry at a discount price. The cards needed 15 minutes to reset, but if you had four you were able to recoup your investment by noon, and the rest of the day was pure profit.

That was one reason they stopped selling the one day unlimited ride cards. Those cards were very popular with folks planning a busy weekend.