Yes you are liable for any damage to an item received, it reveals bad , or insufficient packaging, postal services do not handle items with kid gloves, so it is not enough to post something in a flimsy envelope.
Your buyer could claim for a full refund, so if they are happy to settle for a partial refund, perhaps just the box was damaged? Then, that it is between you and buyer, to agree to an amount. Come back here , if you need help doing this.
Otherwise, if they open a case for item not as described, you would be enforced to issue a full refund.
