I'm sorry, but if that's the case then the snake shouldn't be on the sales floor with a price tag on it. Every shop I know has a back room where sick or unthrifty animals are taken so that they can be treated, kept in a quiet environment so they're not stressed by the flow of humanity wandering by, and they are away from the healthy animals on the floor so that diseases don't spread.
Very true. Paying the store anything for that animal will only encourage more of the same poor behavior if it's the store's fault the animal is in that condition.And, if you were to buy that snake and they were responsible for it, you will simply be encouraging them to do the same again. Sad as it is, in the long run it is better for them to eat the loss than for someone else to pay and then lose it.