Something that I think could really set deckbox apart from other marketplace sites is to allow users to set bid prices for cards in specific sets and conditions. Sellers could browse bid prices and create an order to sell to a specific user for their bid prices, the user then has some time window (say 24-48 hrs) to accept the order and pay for the card(s); essentially allowing everyone to have their own streamlined buylist. Not only does this open up new market opportunities, but could also allow for deckbox to have richer pricing data. You would essentially be opening up a buylist market.

Users already pay subscription fees to sites like quiet speculation just to get a consolidated view of several buylists, this could dwarf that type of service in terms of scope.

That's actually a neat idea. Once you have both bids and asks you could just clear the market automatically, almost.

Yep, we've thought about something along these lines. First implementation could be an option to set a "notification treshhold" for cards in your wishlist. Whenever one of them is posted for sale for less, you'd get an email about it. (Not sure about the specifics yet, just a thought).