To be honest it's kind of sad to see the amount of people which can't actually see the scam. I'm not against people, but due to the fact that most people are silly enough to trust everyone as it is I personally won't agree with such rule being added. It would be kinda a way to solve the problems that encounter, because the participant hasn't thought that it could be a scam what so ever (I'm not say this is the case, just saying how it looks like in general).
As example on #iTrade there's an auto message posted in bold red every 10 minutes about the most "popular" scammers, people yet still get scammed because they don't read it.