Gift cards are weird. They’re supposed to be gifts, but half the time, they feel like an obligation—like, here’s some money, but you can only spend it in this one place. Have fun.

But if you think gift cards are just about birthdays and last-minute Christmas presents, you’re missing the bigger picture. Behind that piece of plastic (or that digital code) is a multi-billion-dollar economy full of discounts, reselling, hacks, and, of course, plenty of scams.