So far I have not been scammed in airdrops, maybe because I just joined very recently.
Or maybe because I only participate in airdrops when it's managed by dev team whom gained my trust.
I believe in the latter reason.
Same thing, I just trust my gut feeling, and don't run for the ones promising just too much. I guess common sense in assessing helps a lot. And so far no disappointments.
Re: topic - wouldn't say that 99% is scam.