Almost all of the things and a way of scamming have already posted above. And that all be enough to say if that is scam or not coz eventually, they are pretty obvious to look at compared to the legit one.
However, I'm wondering why because there still a lot of people get scammed, I don't know if they listening to us or bothered to read any thread concerning about scamming. Or most likely they never changed their mindset but completely just a fool person to think about quick returns, instant millionaire or whatever it is which makes them blind to see it was a scam and they are already been scammed.
From my experience, many people are just to desperate.
They need money because of some urgent needs and they are under stres and can't think in normal way.
Such people are often victims because they "wants" to believe all this "big promises " from scammers.