As a seller on that site , I would have to say, if there was another uk site that had the ability to list items by ISBN/EAN etc, I think that there is an opportunity there. UK forums' confidence is at an all-time low, there appears to be an invasion by US based sellers (with the advantage of low international postage) forcing mass-market items into a downward spiral , and a web development team that appears to be unable to make the simplest adjustment without something else going wrong!
I wouldn't imagine ISBN databases are easily come by. would be good if there was an alternative...
Just a thought!