Hadith no. 2306 (below) is a repeat. Read it here.
Volume 3, Book 48, Number 808 :
Narrated by Abdullah bin Abu Mulaika from ‘Uqba bin Al-Harith (radiallaahu `anhu)
Uqba married the daughter of Abu Ihab bin Aziz, and then a woman came and said, “I suckled ‘Uqba and his wife.” ‘Uqba said to her, “I do not know that you have suckled me, and you did not inform me.” He then sent someone to the house of Abu Ihab to enquire about that but they did not know that she had suckled their daughter. Then ‘Uqba went to the Prophet (sallallaahu `alayhi wasallam) in Medina and asked him about it. The Prophet (sallallaahu `alayhi wasallam) said to him, “How (can you keep your wife) after it has been said (that both of you were suckled by the same woman)?” So, he divorced her and she was married to another (husband).
Volume 3, Book 48, Number 809 :
Narrated by ‘Umar bin Al-Khattab (radiallaahu `anhu)
People were (sometimes) judged by the revealing of a Divine Inspiration during the lifetime of Allah’s Apostle (sallallaahu `alayhi wasallam) but now there is no longer any more (new revelation). Now we judge you by the deeds you practice publicly, so we will trust and favor the one who does good deeds in front of us, and we will not call him to account about what he is really doing in secret, for Allah will judge him for that; but we will not trust or believe the one who presents to us with an evil deed even if he claims that his intentions were good.
It’s plain simple really. Whatever you show people is how they identify you and judge you because they’re witnesses to your deeds. Whatever you hide is between you and Allah.
The other angle: judge people based on what you’ve “witnessed” of their actions. Don’t believe hearsay, it’s not fair to them. :)