Auction laws are different in every state, but simply put, when the hammer drops, it's now yours. There are no cooling odd periods, or chances to have it inspected with any fall back on either the agent or the vendor. Excluding any long legal fights regarding any recent renovations that were sub standard. That legal fight is then against the tradesman involved and limited to a time frame too, depending if you wish to challenge in the Local Courts or Supreme Court.
Either way it will cost you dearly and we both know who makes the money out of court appearances, it's not you, in case you are not sure.