The URL for default domain name for the Auctiva Store, reflects the ID name (just like the dleckington for the one in my sig).
You can change your Store header info like I've done with mine at the Store tab - Store Header.
Here's my HTML code to use as example:
<font size="5">Auctiva Store: 4-Nines Fine<p><font size="3">Proprietor: D. Leckington
If you want that link name to change, I'd do a Support Case to Auctiva and see if they can change your login ID to match the eBay.
Danno