Hilchos Rechilus, chapter 6, section 7

All this was in the time of the Talmud. But in our days, the rulings say that no one should claim that a certain person is as trustworthy to him as two witnesses. So in such a case it is forbidden to accept the story. He may only be careful.

Many people make a mistake here. They are careful about lashon hara and rechilus, but when they hear something from their own family, they believe it, because "they would surely not lie to me." This is a mistake. It makes no difference whether the speaker is someone he trusts or not.