what is the best method to know SCAM [AIRDROPs]
PROJECT
almost all of them is scam and just want to take money from investors thats why they created a token . i suggest not to invest in any of them if you are investors try to find a legit project.
It's hard to find good airdrop, but i'm sure a few of them has potential, for instance Byteball already proved a lot and definitely is one of the good airdrop project. Somewhere on bitcointalk I saw the list of airdrops so it could be useful too. However as you said, the most of them will be probably waste of time