A lot of vendors, in my experience, actually find this quite rude. If you want to make an offer that is lower than listed, make an offer. You obviously like this one better than the cheaper one across the room, so don't even bring it into the discussion. You would basically be asking them to either bash another seller's animal or defend an animal that they probably feel is priced fairly. The seller can either agree to your offer, counter, or say no.
50%?!?! Really?! That isn't haggling. That's just rude.
Remember to shop the quality of the snake, not just look for the cheapest deal.