Jamieson, Fausset and Brown on Matthew 12:23

23. And all the people were amazed, and said, Is not this the son of David?--The form of the interrogative requires this to be rendered, "Is this the Son of David?" And as questions put in this form (in Greek) suppose doubt, and expect rather a negative answer, the meaning is, "Can it possibly be?"--the people thus indicating their secret impression that this must be He; yet saving themselves from the wrath of the ecclesiastics, which a direct assertion of it would have brought upon them. (On a similar question, see on Joh 4:29; and on the phrase, "Son of David," see on Mt 9:27).