See? That's the problem, innit!
Something I've found is common to people who are buying / have bought bootlegs in the past is that a good number of 'em didn't KNOW they were doing it at the time!
Admittedly, it's pretty easy to find out what attributes identify a bootleg as opposed to an official release, but to the casual observer, some bootlegs look pretty danged legit.
I talk to people about this particular problem on a pretty regular basis. I've lost count of how many people have said to me 'Whaaaaaat??? I just checked my anime collection, and there's LOADS of those things!!!'
What I find more surprising is that people are prepared to put up with the generally atrocious quality of most bootlegs coming to UK shores. I've seen a couple of bootlegged discs up close and personal, which the owner had no idea were illegal copies. Both picture and sound were godawful, and the DVDs were so badly put together I was left thinking 'how can anyone think this is acceptable quality for a legit release?' Images played in small boxes on-screen, sound was shot to bits with interference - one DVD even had a start-up menu that was shunted halfway off the screen!
My mind boggles as to why these things find buyers, sometimes.