If I buy or download a song over the Internet that is advertised as legal for use in film, what steps do I need to take to cover my back? The lack of any paper trail in online transactions troubles me. What happens if the owner of the music later changes the license under which he distributes his music? How will I prove it was legal at the time of the transaction? Can he demand the music be removed if he does not like how it was used? What happens if the recording itself is not legal (say, a cover of someone else's music?) Would I still be liable, even if I did not know?

Emre,

I think that's where the saying, 'Buyer Beware' kicks in. Just because the seller says it's a Rolex...

In Canada, being in possession of stolen property is a crime. Even if you thought you bought it legally. Nasty.