To that one cashier:
I think I’m on to your little scam. A couple days ago, my parents bought some stuff at target and got $15 worth of gift card offers. However, when trying to add the gift card to their target account, it wouldn’t accept it.
However, when looking at the receipt, it says “promo gift card: $15. New Balance: $20”. Also, the gift card my parents got has a different number than the one that’s on the receipt. What this tells me is that you scanned an active gift card with $5 already on it, and it combined with the $15 one, and gave my dad a fake inactive card.
Unless it was an honest mistake, but I can’t think of any circumstances that would lead to this.