Fake miners' hardware sellers, runaway escrows, fishing websites and ordinary scammers in sell/buy threads with fake trust ratings and feedback. So many users are losing serious money even when taking necessary precautions. I'm not rich, and these sums would be substantial to me.
Some say that it's the price you have to pay for greediness, but not everyone is a hardcore speculator!
I speculate that for every person starting a thread about getting scammed there are hundreds of people not starting a thread about how they didn't get scammed.
Either that or I've lost my faith in humanity.