Old mp3s for sale

The concept of digital ownership - do you own mp3s? And if you do, why can't you sell them - is getting a bit of a shaping up: a service called Bopaboo has started up, offering a 'used' mp3 marketplace.

I'm expecting the thorny question of how you can tell that an mp3 on sale is the original and not merely a duplicate will bring the pain of a thousand RIAA lawyers down on top of the Bopaboo team at any moment. Which is a pity, as it does offer an answer to the 'what do you do if you buy something rubbish by mistake' question.