Its simple. Compare what the priests or nuns are teaching and compare it to the CCC. IF he or she is not, you bring it to the Church. Where is the Church? Wherever the Bishop is.<quoted text>
*Men are not infallible. Even if they belong to a group "having the fullness of the truth", since they are fallen they could very well mess up that truth, misrepresent it, decide to go rogue and present their own ideas, give their own personal opinions, etc. We do know for a fact it has happened before.
I am a man. I can get things wrong, and have. Last I checked, everyone here is human as well, and can be wrong. Including catholic priests and leaders. As you have educated us about, your leaders are not infallible 24/7. The possibility of errors exists.
Whoever hears the Church hears Jesus.