I posted in your other thread, and the options he's giving you are completely unacceptable IMO. He SHOULD do an exchange if that's what would make it right with you as he was at fault, and giving a discount IS NOT the best he can do to make this right. If you want to go that route then you do what will make you satisfied, but this is just bad business in my eyes.
What was his reasoning to sending you the wrong snake?
May I have the name of this individual so I can not deal with him/her in the future (you can PM me if you want to keep it private while you guys work it out)?