Ok everyone, I think I tracked down the issue... Basically it would appear the default code is calling an array that deals with the specific user (i.e. who you are logged in as) rather than the user you are looking up info on. That's why it works if you view your own auctions but not if you view them as another member who doesn't have any auctions setup.
Open up ebay_hack.xml and scroll down until you reach the member_complete hook. Look for the line:
Code:
if ($vbulletin->userinfo['field38'])
And change it to:
Code:
if ($userinfo['field38'])
Save the file and upload it.
Alternatively, if you already have this plugin installed, go to your plugin manager, locate the plugin "Ebay - Member - Bit" and make the same one line modification I just described there instead.
Hopefully that does the trick for everyone until the coder has a minute to come back and fix this up himself.