That sucks, but also a little fishy.
Its good if it was really cracked and you didnt end up with a bum item.
but if they used it as an excuse because it sold so low, thats a d!ck move.
Its out of your hands now, but id check to see if the seller relists the item later on hoping to get more money. Ive had sellers do the same thing to me before. Tell me the item is broken in some way and I get a refund. Heck, once I even told the seller to send me the broken item anyway and they wouldnt. A week later, it was back for sale mysteriously fixed!.