[Finkevannon]

Allamah Shami has listed 11 instances where criticism does not qualify at Gheebah.
(1) To relate some ones mistake in the vein of regret.
(2) To relate the overall shortcomings of a settlement.
(3) To relate the activities of an open sinner
(4) To relate the deviant beliefs of a deviant to warn the common people
(5) To relate the excess of a wrong doer in front of authority to just ends
(6) To report short coming to an authority capable to stop the wrong
(7) To relate shortcoming of a party in matters of possible future marital alliance
(8) To relate the correct situation while seeking a Fatwah from a Mufti
(9) To relate the short coming of a slave to a possible buyer
(10) To call someone lame or blind for the purpose of introduction
(11) To relate about non-reliable Hadith narrators.

These 11 are not included in Gheebah. Even in these cases looking down upon a Muslim is strictly forbidden. (Ref ...)