I think it differs by state.
In Victoria you get the contract first, and you get a cooling off period unlike auctions. You also get the option of consulting a solicitor prior to making an offer and if you do then you forfeit your cooling off period
You also can negotiate the settlement period but if there are more than one party putting in offers and the vendor wants a longer settlement then you do this could come in to the decision on who to sell to esp if the offers are similarly priced