The Gemorah in Chullin Daf 18a says that if a Shochet doesn't givee his knife to a Chacham to check, we put him in 'Shamta' - I'm assuming this means that we put him into nidui.
The Gemorah then says that according to Rava, we remove him from his position and anounce that what he slaughtered is Teriefah.
The gemorah continues, that the two statements are in agreement; one is true when his knife was actually found to be sharp, and the other applies when the knife is found to have a nick.
So in a case where the knife is found to in fact be good just the shochet didn't show it to the Chacham, we put him in nidui. What is not so in a case where he didn't ask and the knife turns out to be not good that we take him away from his job.
In the first case what happens to the guy? He gets put in nidui however he gets to keep his job and hold his position? Now that he is in nidui (in this situation) what does it mean for him, what disadvantages does he have? People would still buy meat that he shechted?
Yehoshua, Yerushalayim, Eretz Yisrael
Someone who is put in Nidui is allowed to continue to do business. So in the case of the Shochet he may continue to sell his meat (as opposed to someone who is put in Cherem who cannot do business with others except to sustain himself). The person in Nidui, however, has many restrictions on his activities. He may not be counted in a Minyan. He is not counted in a Mezuman. People are not allowed to sit near him. He is not allowed to cut his hair or wash his clothes - similar to someone in mourning. And if he dies while in Nidui the Beis Din places a rock on his casket to represent symbolically that he was stoned by the Beis Din, and no eulogies are said for him. See the Rambam (Hilchos Talmud Torah 7:4) for a description of the all the things that apply to someone in Nidui.
Kol Tuv,
Yonasan Sigler
This is not a Psak Halachah