Read their whitepaper!
Yeah. That simple. You look at how unique their project is and how the community would benefit from it. Then next is the team behind it which is really important if they're legit or not. And you can add a little bit of extra research about it.
This is very true! The whitepaper determines how serious the crypto project is. It explains the technology and tells the purpose of the coin. It tells about the asset. Check also the community, because it is a crucial indicator of the coin's potential.
Although you're right, most scam icos can now imitate a good whitepaper... I am constantly thinking about some ways to automatically moderate these icos but so far, nothing comes up. People should read about these topics and see the scams themselves... We can't help it but see the scammers walk away with the money they gathered most of the time