Are you GST registered?

If so, then 1/11th of the total price (item + postage) goes to the ATO as gst for domestic sales (0 for overseas sales).

Paypal and ebay fees are based on the total (item price + postage) payed by the buyer.

Neither paypal or ebay pay gst so you can't claim gst back on their fees...

If you don't have a store then ebay fees should be 10%, paypal 2.6%, gst 9.09%.

But these are all %s of your total (price + postage) sale prices...

Tax to the ATO will depend on your profits (ie sales - expenses) .....