> As he himself admits, he used a lot of different cards of different values.

And if he wasn't buying the gift cards himself, there's a substantial chance that some of the cards he used were obtained fraudulently (e.g. bought by victims of gift card scams and subsequently sold by the scammers). While there certainly are some legitimate sales of gift cards, there's also a ton of money laundering that takes place, especially when the cards are being sold under face value.