As a merchant I don't like to discount my prices. I believe it says "this item is not worth as much as you are willing to pay for it".
On the other hand, buyers detest shipping charges.
So I will discount -steeply- my shipping and handling charges for multiple purchases, occasionally moving from$10 or $15 total S&H down to Free Shipping.
Sorry for the philosophical answer, but the "race to the bottom" on pricing helps no one, including the buyer .