@ChecklistChikorita asks
I received a card I already own. Is trading it away ungrateful?
Jeff answers
I'd consider what matters to you about that particular gift and any expectations the giver expressed. A duplicate can be kept with a note, used in another collection, or eventually traded. You don't have to make the decision immediately. Gratitude for the person doesn't always require permanent storage of every object.
— Jeff, infinitepulls.com