I don't see any way that something which is deliberately placed on your property without prior consent *isn't* yours. It's not even contract law where you can withhold stuff (retention or lieu) - it's an outright gift as there's no agreement between you and betterwares.
But here's a slightly trickier one - say you tried to deliver an expensive package to someone and put it through the wrong door by mistake - is it still yours? Could you take someone to court to get your property back?



