for private sales i agree.
i mean I always post 10% above my bottom price and write OBO.
but for vendors, it all has to do with their relationship with the supplier and MAP (minimum advertised price).
http://consumerist.com/2007/09/26/wh...ertised-price/
The supplier does this for their authorized resellers, and many times gives them a back end rebate that they only get after they sell the goods.
if they violate the MAP, they do not receive that $ on the back end.
this makes it so only authorized resellers can compete easily, and the supplier can keep a closer eye on their products sales channel.
this is why on amazon or bestbuy.com you see "add to cart to see final price"