Most common mistake is clicking on every link they can find,
i believe i was fooled this way few times but thanks god my btcs were secured.
Also to add to this is the e-books that sometimes are posted on this site. I would not touch them for anything. There is always a reason someone does a ebook vs a post on forum.
Most I think are due to referrral's they use referrals in e-book, and don't have to include non-referral to like on forum. Or the real nasty are hiding malware, but most I think are due to referrals.
But you should always be careful of links you click, or even more so what you download.