Thanks for the information
If this is a commercial seller then you would have the protection under the Consumer Rights Act.
That will require that anything sold is fit for purpose. That doesn't mean perfect but it does mean reasonably good bearing in mind the price paid, the age and condition. If this is a puppy/kitten then it cannot be perfect but it should not have major health issues.
The seller should be liable for a refund.
However, if he refuses then he refuses. He cannot be compelled. All you can do is warn him and if he does not pay sue him.
You can issue here
You should win.
Hope this helps. Please let me know if you need more information.
Can I clarify anything for you?
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