If it's a cancelled or expired card that can just be used for freesat then I would include it, if it's a current card that you're paying for, of course not.
I always thought the sky box remained the property of sky and they could reclaim it at any time. Not that they seem to but if the contract has been terminated by you they may want it back.
It looks from googling as though you can get the free to air channels without a card, but would need a card to use the box for recording. If I hadn't specified "includes a card" in the sale details, then i would send without.