Jǐnguǎn tā yánzhī-záozáo, dàjiā háishì bànxìnbànyí.
Although she spoke with conviction, everyone was still only half-convinced.
Tips
history
From Pu Songling's Qing collection 《聊斋志异·段氏》: 言之凿凿，确可信据 - the author vouches for a ghost story by the teller's emphatic certainty. The doubled 凿凿 (literally 'chiseled-chiseled') carries the sense of hard, fixed, undeniable.
usage
Tone is often skeptical - the listener notes the speaker's certainty without necessarily sharing it: 尽管他言之凿凿，证据却不足. For straightforward conviction, 肯定 or 确信 are neutral alternatives.
