Psalm 146:3

Do not put your trust in princes, in mortal men, who cannot save. 

This Psalm doesn't mean to not let other help you or to not engage with others. It also doesn't mean we should suspicious of everyone we meet. In this case, trust means our spiritual trust. The health of our spirits cannot be achieved through trusting mankind. Many these days seek spirituality through meditation and in trusting gurus or self help experts. This may enduce a feeling of spirituality but true spiritual health can only be gained through trusting GOD. We have to realize that when we meet people who help us on a spiritual journey, they are actually sent to us by GOD.

Its OK to trust others as long as we know that if they are a positive influence in our lives, they have been sent to us by GOD, who we can always trust with all our hearts.