I didn't know there are sites that provide airdrops updates
You can google everything that you want to know including those airdrops. I did the job for you and here are the few websites that came out.https://airdropalert.com/
https://www.ico-check.com/ico-airdrop
http://www.airdroptracker.co/
i hope they are legit 
What you should doubt are those airdrops if they are legit. There are cases that they are asking for a payment before you get those airdrop tokens.