How will you defend yourself, your family, and your worldly belongings following an apocalypse? Sure, it is easy to say that you will shoot anyone that comes close but could you really do it? Moreover, have you thought of alternative methods to defend what is yours such as setting up blockades or no-enter zones?
Trust is something earned and even though it may feel instinctive, be wary. It is okay to put strangers through some tests and even then, be conservative in doling out trust cookies.
No surprise here. Just be prepared to evaluate, interview and act based upon as much knowledge and gut instinct you can muster. Trust no one until that trust in earned. Start building your criteria for trustworthy-ness starting today. Practice your interview questions and learn how to say "no" if you have to.
Learn to take advantage of those moments now, while you can hone your skill at recognizing those opportunities.