First of all. This isn't my idea.
Sorry if this has been posted before
But here is a theory
You know all those fake files that are turning up on kazaa networks?
This might work.
Go by the file name. If it has a number next to it, don't download it.
And now the obvious - Go by the amount of users. If its a popular mp3, you will not even have to do "Search more" you will see the difference in the amount of users that are sharing the file.