There are even people on EBay that google, see the picture and read the specs under it and think this was the only model ever built.
I won a Dual 2,7GHz, which turned out to be a Dual 1,8GHz with only four RAM Banks (so not only a 1,8GHz model, but even one with only 4 RAM Slots).
The seller said, he didn't know, but refused to take it back and claimed, since he said in the auction text, that he would not take it back, he was on the right side. The end of the story was, I discussed over 2 months with him (already took effort to get him to even send the Mac, which was still considered to be a Dual 2,7GHz at this time) and had to thread with police and stuff (though I am not that kind of guy, I am very nice to people actually

).
He was so stupid, that I was able to google his school, he had just left, his amazon reviewer account and facebook account. It turned out, he was a pupil living in a part of Berlin (Berlin-Neu-Kölln), that is known for social tensions and all that stuff.
The other time a won a Quad from a graphics agency, that turned out to be a 2,3GHz DC.
If I am interested in something, I now always ask them to send me the serial or specification code at the bottom of the housing (or on the back in case of PM G4s) or