So far I've done a little work on the back end but that isn't visible so today I thought I'd start working on the interface, how it will look.
This is a work in progress and I'm looking for input, what do you want to see listed near the items?
So far this is where I'm going with it:

As you can see in the image stuff will be listed two at a time, so think about the way our shop looks but instead of 4 or 6 items per row it will have two auction listings per row. You will scroll down to view more listings.
There will be a way to look at specific categories and filter by a search system. And of course a way to add items from your in-game inventory. To keep listings simple I intend to offer the following ways to list (For sellers to use):
Time: 12, 24 and 48 hour listings
Type: Bidding only, Buying only, Bidding & Buying
Stack Sizes: Up to 64 of the item you're listing (You can select any amount from 1 to 64 to list)
The listings you place will cost money, the shop will adjust how much it charges you depending on how much you list the items for, how long you want the listing to display and the stack size but I doubt it will be more than a few rickies.