Liars when they speak the truth are not believed. Aristotle
Liars are always most disposed to swear. Vittorio Alfieri
He who does not bellow the truth when he knows the truth makes himself the accomplice of liars and forgers. Charles Péguy
One witness one liar; more witnesses, all liars. Greek Proverb
Beware: some liars tell the truth. Arabic Proverb
Liars should have good memories. Italian Proverb