Well, besides wasting time, as long as you are not giving the airdropper personal information, your private key or money, there isn't so much to lose. But as others have said before me, things to lookout for in a non-scam project are: a real team with experience, a reasonable roadmap, a whitepaper, the coin/token addresses a real need (so it isn't useless). If you consider all of these things and use your head, you should be able to avoid scams are plain old garbage projects.