Albert Barnes on John 4:29

Is not this the Christ? Though she probably believed it, yet she proposed it modestly, lest she should appear to dictate in a case which was so important, and which demanded so much attention. The evidence on which she was satisfied that he was the Messiah was that he had told her all things that she had done--perhaps much more than is here recorded. The question which she submitted to them was whether this was not satisfactory proof that he was the Messiah.