Do ebay charge comission on postage? if not then bumping up postage sounds like a legitimate way of keeping costs down.
As for myself posting something like that, I would probably charge something like ?20, not because thats what the stamps would cost me, but because of all the damn hassle it takes to get the thing properly wrapped and to find a carrier.
Remember not all of us run mail order buisnesses, not all of us have all these ducks already lined up, not all of us have the necesary materials on hand, so I think its quite justifiable for us mortals to charge quite a bit more.
Surely anyone who buys on Ebay takes postage into account when hes making his bids, I know I always do, and Ive noticed that on popular items the final selling price often evens out when you include postage.
just my 4p worth