I'm ambivalent about buy/sell facility, but do feel the urge to mention 20 million Australians do not represent the voting populous.
I've given heaps of "stuff" away via the PM system and note PPRune DO have an advertising section, however costly that may be for David Clark gel seals or Ray Ban's. (do they still have them)?
PPRune do have an excellent readership though.
Depends what you want to buy/sell I guess and how much you want to pay.