All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
If the buyer left the animal in the seller's possession as a trust or mortgage and it was harmed with neither negligence nor transgression, the seller is not liable; rather, the buyer is. The seller in this case is a trustee and he is not liable for any damage caused to the trust as long as there is neither transgression nor negligence on his part.
If the animal died before being delivered to the buyer, the latter is entitled to take back the paid sum of the price because the sold item is still in the seller's possession.
Allaah Knows best.