So HE made a mistake refuses to fix HIS mistake and offer a discount on the next purchase, sorry but if it was me there wouldn'tīt be a next purchase.
The only acceptable compensations to me would be.
A/ Replacement of the animal and getting the one originally purchased.
B/ If you are willing to keep the animal, getting a partial refund on the animal you just purchased.
C/ Return of the animal at HIS expense and full refund including shipping fee.