Most recently a Rav disqualified a potential witness for a Kidushin.
The Rav is a Magid Shiur in a respected Yeshiva in E.Y. and a Rav of a Beis Knesses in Northern E.Y.
The Rav knew the designated witness and knew that on a number of occasions he was a "Kofuy Tov" to people who gave him Great opportunities.
The Rav asked that they not use this witness and explained himself.
He said that he heard from a Gadol BeTorah that Maran Harav Chaim Ozer Zt"l considered a 'Kafuy Tov' someone who deserves to be a "Psul Kahal"! He based it on the Ramban in Parshas Ki Tetzei.
And the Rav added “Someone who deserves to be a "Psul Kahal" should not be a witness”!
Utenu Kavod L'Torah!