It is mentioned in hadeeth that one must not talk bad about dead people.
However the reward and punishment are related to what people talk about which was true! We are Allah’s witnesses on earth and if we talk good about people who had died without lying, this means that this person is generally good at the side of Allah.

Here some people says that once a person died, we should not talk bad about him cause for our bad comments he would get bad treatment. On the other hand if we talk only good about dat dead, he would get reward from Allah for that. Is that true? If yes, there are people who have two faces what will happen to those.