According to Bernard Lewis, "in the early Islamic centuries there could be no better way of promoting a cause, an opinion, or a faction than to cite an appropriate action or utterance of the Prophet." This gave strong incentive to fabricate hadith.

How do you identify a fabricated hadith?

It may contain accusation on the Prophet or his Swahabas. It may be illogical and not appealing to reason. The narrator is not a pious Muslim. It may contradict of he hadith on the same subject.

What is the purpose of having false Hadiths in hadith collections?

Candidates need to give their personal view as to why it was essential to include false (mawdu) Hadiths in Hadith collections. It could be said that they were included to ensure that the possibility of them being categorised in the other categories, e.g. sahih, hasan, etc. did not occur.