Not sure if this has been resolved yet. If I were you, I wouldn't refund anything that died after 72 hours. From what I have seen, that seems to be the most amount of time sellers guarantee an animal for. Furthermore, if this guy really has been in the business for 17 years, he would know that most people certainly would not offer a refund after two weeks, because at that point, there would be too many possibilities as to what could have happened.
I invested in many, many snakes over the past several years, and I take them to the vet when they aren't doing well. I treat them, and sometimes they just don't make it. I have also had snakes randomly drop dead with no warning signs whatsoever. I never went after the seller because I am aware these things can happen. Had the snake arrived with something suspicious, or any type of sign that showed it was possibly not 100% healthy, then it would be a different story. You can do everything right, and sometimes it's just not enough. Furthermore, he praised you upon receipt of the animal, but then two weeks later after it dies, he suddenly accuses you of shabby packaging skills. If there were really an issue with the packaging, I would think that it would have come up before then.
Just my two cents....