For anyone interested, I have scored a small victory on this front.
After a few months of reporting ofending plant items on both oztion and ebay, ebay management has implemented a policy that prohibits the sale of any exotic plants species that are listed as noxious weeds any where in Australia. Oztion is also condisering implementing a similar policy.
Ebay management is also considering banning the sale of any exotic plants that appear on the World Wildlife Foundation list of invasive exotic species. Don't know how far we will get with this.