Possible the buyer? I don't think I'd be too happy if I paid for a laptop with, say, Windows XP, and it turned out it was pirated.
I'd contact the police and give them the name and address of the seller, personally.
It's happened to me before but the seller disappeared, it was probably one of the most frustrating things that's happened to be unable to track him down and punch him in the mouth for conning me.
if you're happy with paying for pirated software, that's up to you ... I'm not.