Sometimes you can't even predict if they can truly pay or not. That's how good this scam airdrop developer and promoter has turned out to be.
 
But one place I usually look at is how greedy the project appears to be in terms of sharing their tokens with their airdrop promoters.

To those who make fake promises and still give out a bunch of their tokens, promising to turn every participant and early investor into wealthy holders automatically turns into a red flag for me.