Radak (8): Also Shomron, now the head of Efrayim, and Ben Remalyahu its head, will not last long - "Yisa Es Cheil Damesek v'Es Shalal Shomron Lifnei Melech Ashur" (below, 8:4). "U'She'ar Aram ki'Chvod Bnei Yisrael Yihyu" (17:3; Melech Ashur will exile Aram at the same time as Efrayim - Radak there).

Malbim (8-9): The evil of Efrayim is known from the evil of its capitol Shomron and its king Pekach. They did not change their ways; Shomron is still the capitol and ben Remalyahu the king.

Rashi: If you, Achaz and his nation, do not believe my Nevu'ah; I know that you are Resha'im.

Radak: The Navi says, if you do not believe my Nevu'ah, it is because "Lo Se'amenu" - you are not trustworthy and believers in Hashem.

Malbim: The Navi saw that he does not believe his word. He became angry - do you not believe Hashem's word because "Lo Se'amenu" (you are not trustworthy)?!

Rashi: There is no faithfulness in you.

Radak: Se'amenu refers to endurance, like "Meimav Ne'emanim" (33:16). Also refer to 7:9:2:2.

Malbim: Refer to 7:9:2:3.