I think your offer was more than fare. Unless he bold face lies... anybody who is considering buying an animal from you that hears you are giving 30day guarantees will def still buy from you. What he might leave out is that he waited 4 months to contact you about the "sick" animal. But in that case you could have sent him a prefectly healthy animal and told people not to buy from you just because he wanted to be a (for lack of a better term) Shmuck. You send him a refund.... then people who have had animals that might have been sick for more than 4 months will be calling saying "but you did it at 4 months or whatever for that guy" stick to your guns dank...
IMO you wont loose business or any kind of reputation for being more than fair.
