Are they still within 30 days of the item's last estimated date for delivery? Then, they are entitled to a full refund.
Ask them to open a case for item n ot as described. Accept and send a pre paid label for the return of the item, within 3 days, and only fully refund when the item is back with you, refund through the case details. Stick within the timeline and your seller fees will be refunded, and your seller performance not affected.
They will have to provide a photo when replying to the case, but do not have to oblige to send packaging back as this may well have been thrown away on opening the item.