Hi Kimmy,
If you purchase a custom domain through Auctiva, your buyers will be able to reach your Auctiva store by entering that domain into the URL field of their browsers. Your Auctiva store is a customizable storefront that displays all of your active eBay listings at any given time and can also be reached by clicking the link on the bottom right of your store window.
By including your Auctiva store domain in all of your customer communications, and promoting it wherever you can, you should be able to direct more traffic to your Auctiva store and, consequently, generate more sales. A custom domain can convey a more professional image and stand out more to customers than the default Auctiva store URL, "store.auctiva.com/{user_name}, so more customers will likely visit your store if you are using a custom domain.
-Mike