If eBay buyers were rational, they would add the purchase price of their goods to the postage and packing before deciding whether or not to buy and how much to bid.

And eBay buyers are rational, right?

Not particularly, say two California academics. They held 80 auctions of CDs and computer games and varied the reserve price and additional costs, just to see what would happen.

"...lowering the opening bid price while raising shipping charges attracts earlier and more bidders and ultimately leads to higher revenues compared with doing the reverse. Those findings suggest consumers pay less attention or even completely overlook shipping costs when making bids, the professors conclude.

...the results could have implications for fixed-price retailing, including electronics and books, where it’s also common marketing practice to divide a price into two pieces. Framing the same price as the total of different attributes may significantly affect consumer behavior, Morgan says."