I had another car I was looking at which the seller said he was selling it for a friend which I have found out is code for stolen.
About 10 years ago I was checking into a car that was local to me for a friend who was about 5 hours away. The seller told me that he wouldn't even answer questions unless the potential buyer asked them. When I told him that the buyer wasn't very knowledgeable about cars, so all the early questions were going to come from me anyway, he started yelling at me "I know what you people try to do! And you won't do it to me!"
To this day I have no idea what he was talking about. But, he did call me back the next day to say that he "knew" that I was the same person who had looked at his friend's car as well (I have no idea what he was talking about there either). I told him that if I got another call from him I'd report him to the FBI.