Well, most cases you listed are well-documents and have been known among airdrop bounty hunters. Never pay anything just to receive the airdrop, never sign in something dubious just for airdrop, and never click any link in email if you don't know who's the sender. Follow those rules of thumb and you will be safe.
Scammers have been using email a lot to send phishing links to all email inboxes and masquerading as official project accounts, so you need to provide an alternative email to sign up for bounty and airdrop programs to prevent the main email from sending phishing messages.