I've listed several items for sale and given the postage cost according to the size and weight of the packaged item.
One item was listed with a postage cost of £5.21 for the weighty parcel, but upon selling, ebay has charged the buyer £2.85 instead.
It's not a great loss in this case, but with little profit, it makes a difference.
How is it that Ebay can just arbitrarily charge the buyer less for postage than the price quoted in the listing?