Ahh, sorry, my mistake. I didn't see that you are in Australia. Here through USPS you have to use Priority Mail or higher in order to get insurance, which effectively means US$25 or more. Not feasible for single-stamp/cover shipments, as buyers won't pay for it.
However, there are 3rd party insurance companies (Shipsaver, Shipsurance, etc.) that you can sign up with that don't have the same limitations. They will insure international 1st class shipments, as long as there is tracking.
I would assume (perhaps erroneously) that there are also 3rd party insurance companies in Australia? They really give sellers more flexibility and protection. At the end of the day you have to protect yourself, as
ebay and PayPal sure as hell won't...