To me it just depends on the situation.
See, these guys who post a lot on Kingsnake and such get a lot of really low-ball offers and offers from people who have no intention of actually buying the animal. After a while it gets old, and thus the refusal to make a deal.
I have found if you are sincere about a particular animal and start a conversation with the seller, sometimes you can negotiate a deal. But if you start out by asking for a lower price, you'll usually get ignored.
For example you find a really nice let's say Firefly female. The seller is asking an average market price for her and says his price is firm. You contact the seller and ask the intelligent questions. What does she eat ? When do you feed ? When did she hatch ? What is your shipping policy ? What forms of payment do you accept ? Tell the seller why you are interested in his animal instead of a different seller's animal, be honest.
Once you get a good conversation going, ask what the price with shipping was again. Sometimes the seller may quote you the advertised price, and offer a shipping discount. Sometimes the seller may agree to come down a smidgen on the price if they feel you are serious. Sometimes they won't.
But ask yourself this, if you posted one of your own snakes, for what you knew was a very reasonable price, and all you got were 25 emails a day offering you less than 1/4th of the snakes value, how likely would you be to want to discount right off the bat ?
Gale