One of the most important skills a person can have is the ability to recognize error. Sometimes this is pure evil; more often it is a mistake. A mistake can be a simple typo or miscalculation, or it could be the result of a decision based on insufficient, or incorrect information. Sometimes it is the result of trusting the wrong people, and giving credence to information without checking it for correctness. When the error is evil, it does not usually present with horns and a pitchfork. More likely it is a suggestion whispered in the ear.
So how do we recognize error, of whatever sort? In the long run, "By their fruits ye shall know them." In the short run, we usually consider the historical reliability of the source, and compare it with relevant data from other sources. Critical thinking can be of immense help, but logic alone is not sufficient. Nearly anything can be justified with pure logic; sometimes it has to be overridden by the heart. For example, some people are trying hard to normalize paedophilia, styling it as "man boy love" or "age gap love" or other such innocuous slogans. I like to think that anyone with a shred of empathy rejects it as abominable.
What to do when we recognize error? It depends. If it is our own error, we want to correct it immediately, and avoid it in the future. If it is an imposition on the public, we want to be faithful in pointing it out so that others will not fall into the pit. If it is an individual, it depends on our relationship and the exact circumstances. Gratuitous advice may seem like the loving thing to do, but more often than not it is unappreciated and thus not advisable. In any case, correction of others needs to be done with humility, in the spirit of Galations 6:1
"Brethren, if a man be overtaken in a fault, ye which are spiritual, restore such an one in the spirit of meekness; considering thyself, lest thou also be tempted."