I made someone a $6 offer on a card he was asking $8 for. He raised the price on site to $14 and countered at $9.50. At least he countered - on the three occasions I've made offers to Joel SS, he's simply declined and raised the price of the card. Twice I was able to buy at a price I wanted off someone else.
Now, they're the seller's cards and they can ask what they like. I just think the raise-and-counter-above-initial-asking-price move is low.