You will not be able to spot them easily. You need to understand first what is the project and how does it work, of course they should have a whitepaper where all the details about the project is included and as an investor you need to understand those and by reading it alone you will see how the investment works, what happened to their end and of course you will find some shady or skeptical things and if they have those things they are not yet a scam but a skeptical one and should stay away from it as soon as possible.

It's better to stay away to some skeptical investment project rather than wait for it to become a scam.