They were bunch of fake account abusing discount code in gameflip market using multiple account they created. You should look up and clean your market from this abuser with bunch of fake account. This happen since long time ago but still no action yet. They keep selling same item at all times someone must stop this abuser.
Because this thing gonna make coupon code quota for everyone reducing drastically. And with spamming or abusing posted list no one will get benefit from their sale.