Then there's Bernie Madoff. This one's a stinker, for so many reasons. A lot of people are going to get hurt. People who never had anything to do with his Ponzi scheme are going to get hurt. He probably didn't mean to hurt anyone. These guys almost never do. They never think it's going to catch up with them and once it starts to go bad the efforts to patch it, hide it, fix it until things get better (but they never do) just snowballs out of control. I've seen this before. Everyone loses.
Relevant cliché of the day: if it looks too good to be true, it is. Take a deep breath and walk away.
Then again, sometimes even a really bad deal is actually worse than it looks.