Hi Salcey Saddlery,
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. To do this, go to Auctiva -> Store(tab) -> Edit Items. Items that are made hidden will not be shown in your store window the next time it refreshes, which it does about every 2 hours.
I hope this helps=)
-Mike