Hi Crimsonsteel,
The store window is set to display 14 of your active listings at a time and is refreshed every 2 hours. Each time the store window refreshes, it is populated with another 14 of your current listings that are ending around the same time as the next auction of yours that is viewed.
The only way you can control what goes in your store window is by making items hidden, which can be accomplished by clicking the "Store Items" link under the "Store" tab within your Auctiva account. Any items that are made hidden will no longer be displayed in your Auctiva store, nor will they be displayed in your store window the next time it refreshes
-Mike
