It's genuinely a difficult question because there are projects that have the exact same technical designs that are still legitimate projects. So how do you evaluate this? From my perspective it used to easier. I'd just look at the problems that the company was focusing on and ask: (1) are they solving a real issue (2) are they making a valid contribution with their solution?

Normally both 1 and 2 would be eliminated as projects tried to intentionally use buzzwords to confuse investors into thinking they were doing something cool. They would write papers that mentioned nothing specific and you would sometimes come away thinking: 'what the fug are you even building' or often 'this exists already so what is your take on it?' The latter of which is hard to deny because many tokens, ICOs, blockchains really don't need to exist. Technically you could have argued that Ethereum didn't need to make a new blockchain because a third-party system could have been made that added smart contract logic on top of Bitcoin like a soft fork. This would have been similar to master coin.

I'd say that the quality of the people around a project can tell you a lot. Often scammers use impressive sounding publicists to make them seem like they're successful entrepreneurs. But when you dig deeper its all just paid shilling.