Watch for Compilations that are “Too Good to Be True": Many pirates make “dream compilation” CDs, comprised of songs by numerous artists on different record labels who would not likely appear on the same legitimate album together.
So, if you see an album with all of your favourite artists on it, performing the songs you love, for the love of God don't buy it -- it's probably pirated!
Seriously, this is their press release. And in it, they explicitly state that pirates are putting together products that people want more than the legitimate variety. This, of course, is why teenagers should be sued in to penury, rather than something as revolutionary as the music industry putting together its own compilations that people want to buy.
Related: The Year the Music Industry Broke.