Anyone who claims the GST on their postage will be paying more if printing out the postage labels in eBay.  Australia Post pricing includes GST.  I claim back 10% of my postage account with Australia Post for the GST component.  Any seller who does a GST return would be stupid to print out the eBay labelling when there is no GST invoice supplied  by eBay thus effectively paying 10% more for postage.