The faithful have a sixth sense that allows them to sense the insincerity of people who hide their immorality from them. This sixth sense comes from Allah and allows them to recognize a person's state of morality based on their behavior, words, and the impression they give off. It is not something that can be explained with evidence, but it is felt by everyone in the room. The faithful can also tell when someone is speaking insincerely, and it is important to be honest about one's wrongdoings.
Allah alone knows the unseen, but He grants His faithful the ability to sense insincerity. A person of faith is aware that mistakes can be made, and that Allah is the only one who can truly judge someone's heart. The faithful remain cautious when forming impressions about the sincerity of others, understanding that these impressions are not evidence. Instead, they take any necessary measures to protect themselves from possible harm, knowing that only Allah can know the truth of a person's inner intentions.