have one's doubts

be apprehensive of be curious be dubious be in a quandary be puzzled be uncertain be undetermined call in question challenge demur disbelieve discredit dispute distrust fear fluctuate give no credence harbor suspicion have qualms hesitate imagine impugn insinuate misgive mistrust not buy query question read differently scruple shilly-shally skepticize smell a rat surmise suspect take dim view of vacillate waver wonder wonder at