What about if someone left it out for a mate to pick up ?
What about if it was a private sale and someone left it outside of the persons house, but ya mate picked it up before the owner got home. ?
What if someone broke in and tried to steal it but it was too heavy for two small blokes to put in a truck and they left it there.?
What if some idiot delivery driver got the shits n dumped it there cause the people werent home. ?
I would be knocking on the persons door and asking if it is 1 million percent legitimate. In QLD there is a law against taking anything without express permission. Its legally called "Stealing by Finding". Being in security,  I wouldnt sleep at night til I knocked on the owners door.