Where a person purports to sell property belonging to another without proper authority, and executes a sale agreement falsely representing themselves as the owner/seller, such an agreement is a nullity and cannot transfer valid title to the purchaser. When the lawful owner challenges such a transaction, the onus lies on the purported purchaser to prove that there was a genuine, authorized sale. Where the purported sale is predicated on a patent nullity and the purported purchaser relies primarily on inadmissible hearsay evidence to prove authorization, they fail to discharge the onus and the sale will be declared unlawful.