Not being stupid is no defense against being conned. On the contrary, a truly stupid mark isn't going to understand the scheme; an intelligent person will immediately see the way they stand to benefit. It's the willingness to cheat that gets you in trouble.
You need to be not stupid stupid, but reading these articles it is pretty clear that the marks are not "smart" if they're investing in something they don't understand.
The truly intelligent person will see the way the other person stands to benefit. That's how you avoid getting scammed. Unless you truly believe some stranger is offering you this great opportunity out of the goodness of their heart (in which case you have a thing or two to learn about people in general).
And if I can't understand how the other person benefits? I'm immediately suspicious.
This is not really a factor. A good scam involves the scammer and the mark going in on something together. What the scammer (ostensibly) gets out of the scheme is part and parcel of the pitch.
Check out The Big Con by David Maurer