I know the speed of the AH is supposed to be addressed, but I can't help feeling like there are a couple more things that would make dramatic improvements in the usability area.
First, I think it would be helpful to have more information about what cards you have up for sale and what bids you have for cards in the regular buy/sell screens. It's cool that you have a badge to indicate when you do, but it would be more informative (since you can see what the current low price/high bid is to your right) if you could see the price of your current offer in the badge somewhere or maybe somewhere else. I know I can't always remember if the number to the right reflects my bid or if I've been outbid and need to do something about it.
Also, it would be killer if I could bail on my sell offer from the buy screen and vice-versa. I can't count the times I've put in a thoughtful offer for a sale and then begun looking through the buys only to find that the usual suspects have come right behind me doing their hourly "subtract a credit from the lowest bid on every card in the AH" routine. At which point, I'll usually just decide to wait for a more favorable day to sell. But, if I've got a lot of cards out there, I have to either remember or write down every single instance or else go back and forth between the buy screen to the my sales screen so I can cancel or update my offer. More often than not, I just end up canceling every single one and starting from scratch. Kind of annoying.
This is even more important for the other way, where you can have a considerable amount of credits tied up in buy bids that aren't going to see the light of day if the card isn't one that gets heavy volume.
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