Sell it anyway. The contract of sale shows that the purchaser takes it with all faults, patent and latent. Note that the purchaser has more protection buying a handkerchief than buying your property.
Not according to this article, and others: https://cmlaw.com.au/unveiling-the-truth-navigating-vendor-disclosures.
The purchaser could easily prove that the vendor knew of a problem that would have affected their decision to buy.