I really hope you do give this man his refund and, yes, I understand your thought process that there is no definitive proof on who injured the snake though, in all honesty, it more looks like her tail was caught in a packaging error than anything else. This is just my opinion. Now, I would like to add something ...
Clearly, you are the one who is missing the point about the BOI.
You are not on the BOI for possibly being the one who injured the animal while packing it. You are on here for your lacking professionalism, inability to perform proper customer service and failure to take responsibility for even your own words. To say you simply acted incorrectly is an understatement.
But I am ust an outside observer looking in. I do not know you and I do not know the customer.
Now, let me explain something to you. While you may have some "Good Guy" threads about you and you may have had numerous successful transactions before this one, this is why I would not even think to buy from you:
1. You made a mockery of this customer and acted as a child would when caught with their hand in the cookie jar. You laughed at everything and made ridiculous comments that were suitable for a first grader's insult book.
2. You admit to not being a pro and, therefore, desiring not to be professional. Anyone who sells anything should never have this mentality because it is an immediate red flag to someone that just does not care about anyone or anything but himself. If you are in this business then you be professonal or else you end up on the BOI. Deal with it.
3. You are mocking your customer for sending you partial payments as if that is supposed to mean anything. You are the one who agreed to let him do it, so why turn around and act like you are so much better than him because of it? Regardless? You owe him one of the two payments he sent you anyway, so that little snippet of your being a sarcastic fool just leaves you looking like an immature kid.
4. You get really aggressive towards people and then, a few minutes later, apologize and try to make nice, but when that does not go your way, you get aggressive again. Seems to me you are a rather unstable individual.
5. You guarantee customer satisfaction (something a professional would do, mind you) and then fail to successfully follow through with such a plan. I guess customer satisfaction to you is limited to those that do not complain.
6. You spend money you do not have before time (money is not yours until the deal is done and the customer is satisfied) this is a rather big "no-no".
7. You think that people are judging you as a person, we are not, that is not the purpose of the BOI. The purpose of the boy is to hear business practices of people who are in the business of reptiles and to make an informed and educated decision on if we wish to deal with that person. It does not matter if you were doing missionary work in a third world country or saving homeless children. That is irrelevant to your business practices.
So, to sum up for you ... you are immature, you lack professionalism, you think this business is a joke, you are irresponsible with transactions, you are quick to anger, you use petty jokes when you should be serious and you fail to take responsibility for yourself. That makes you the poster child of who not to do business with, in my opinion.
Again, I hope you do give this man his money back and this issue is resolved, but understand, this thread being posted did not harm your reputation. You did.