Offering to sell an illegal drug is against the law in Australia. It doesn't matter if you intend to actually complete the sale, you are actually in a position to do so, or if what is sold or supplied is not an illegal drug. All that's required is that you offered the drugs and you meant the offer to be taken seriously. In NSW, if you offer something for sale claiming it is an illegal drug, it will be treated as if it was that illegal drug. In WA if it can be shown that you thought you had an illegal a drug, and you didn't really, you can still be convicted of a crime.
Then law states a specific amount of each drug over which you are assumed to have intent to supply. Over this and you have to prove it was for your own use. In any case the prosecutor could lead other evidence to suggest you had intent to supply - eg if you had everything in individual bags or if you had scales.