Because I listed the card for an inflated price to begin with. Since they had no intention of actually paying for it, they "bought" it. Which in the end, backfired on them.

Ah, that makes a lot more sense. Without that detail, it sounded like you were effectively blackmailing the scammer's parents rather than just getting paid the agreed amount.

Updated to reflect that. Though to be honest, I could have told his mother twice the amount, when she asked how much does she owe.