I'd have to go with the consensus and say you need to honor the deal. Me, personally, my word is my bond, regardless of money being exchanged or not or the amount. I guess it comes down to what you feel your integrity is worth: the monetary value of that animal to back out of the deal or seeing a "special" snake go but knowing you did the right thing? I can't put a price on my integrity and wouldn't ever care to try to.