What is "Tiflah"?
Radak: This is like "Nevi'ayich Chazu Lach Shav v'Safel" (Eichah 2:14), "v'Lo Nasan Tiflah" (Iyov 1:22) - something inferior without taste.
Malbim: They did not sin b'Mezid and with scheming, just they lacked reasoning and understanding, and erred about Ba'al. They thought that Ba'al gives Nevu'ah to [its prophets], and it is real.
When did Hashem see Tiflah in Nevi'ei Shomron?
Rashi: It was before they were exiled.
Why did they prophesize in the name of Ba'al?
Radak: Achav served Ba'al. Many false Nevi'im prophesized in its name - 450 in Achav's day; Eliyahu killed them. Afterwards, others arose; Yehu killed them. They made Yisrael err, until they were exiled in their sin. However, in Yerushalayim Nevi'ei ha'Ba'al did not arise. Malchei Yehudah did not serve Ba'al, except for Menasheh, and afterwards he repented. "Hinab'u" should be Hisnab'u (Hispa'el conjugation); the Tov is omitted.
