if you think they aren't worth that much, start selling the items cheaper. There's nothing stopping you from undercutting the other sellers.
if I am looking to buy, then I don't have one, and I won't buy until common sense comes to exchange posters... which leaves you continuing to post the item over and over again when it expires and me compensating in other ways. No one wins
If I put something on the Exchange, I tend to price it at least about 75% of the value displayed in the tool tip. I figure, since I was going to discard it for 50% anyway, I might as well see if anyone else wants it, and make a few more EC.