How to not deceived by scam?

Basically, if it seems to good to be true, then it probably is. Use your common sense.

first ,they are strenger mostly ,and they are very zest for you in something but have no reason .and other kind is they strenuosityly to boost some idea or something to you .but how tonot deceived by scam ? my way is never to believe any distrustful persons and nver think taht there's a free dinner for you .