What is secrets airdrop ?
There's no secret in airdropping, the method is known by everyone and we are aware that most of it is a scam.
why distribut the token is free ?
That is part of the advertisement so they are giving it for free and it becomes effective when there are too many people joining that airdrop.
How I know the trusted airdrop ?
It's not easy on this era, you have to trust the team otherwise there's no way to know it.