If you are unsure if your specimen is a fly, you may need to consult a key to the various orders of insects. A key to Australian insect orders can be found here.
If definitely a fly, it may be useful to check your identification against a key containing a greater range of dipteran taxa. A key to the families of Diptera may prove useful for ensuring that your specimen should actually be identified using the current key. McAlpine (1981) and Oosterbroek (1998) provide excellent keys to the families of Diptera, but they can be challenging to use.
Wallman (2001) also provides a key for carrion breeding blowflies in south-eastern Australia, however, similar to the current key, it can only be used to identify adults reared from carrion. Pont (1971) provides data relevant to the species of Australian Muscidae found in carrion.
Hamilton, J. R., Yeates, D. K., Hastings, A., Colless, D. H., McAlpine, D. K., Bickel, D., Cranston, P. S., Schneider, M. A., Daniels, G., Marshall, S. 2006. On The Fly - The Interactive Atlas and Key to Australia Fly Families. Brisbane: Centre for Biological Information Technology.
McAlpine, J. F. 1981. Key to Families - Adults. In: McAlpine, J. F., Peterson, B. V., Shewell., G. E., Teskey, H. J., Vockeroth, J. R. & Wodd, D. M. (eds.) Manual of Nearctic Diptera. Ottawa: Research Branch, Agriculture Canada.
Oosterbroek, P. 1998. The Families of Diptera of the Malay Archipelago. Leiden: E. J. Brill.
Pont, A. C. 1973. Studies on Australian Muscidae (Diptera) IV. A revision of the subfamilies Muscinae and Stomoxyinae. Australian Journal of Zoology Supplementary Series, 21, 129-296.
Wallman, J. F. 2001. A key to the adults of species of blowflies in southern Australia known or suspected to breed in carrion. Medical and Veterinary Entomology, 15, 433-437.