Shaykh Ibn Abd al-Wahhaab said (7/25) in his letter to Muhammad bin 'Eed:

As for what the enemies have mentioned about me: That I make takfir on the basis of presumption, and on the basis of loyalty, or that I make takfir of the ignorant person upon whom the proof has not been established, then this is a mighty slander. They desire to make the people flee from the deen of Allaah and His Messenger by it.

Notes

Here Ibn Abd al-Wahhaab rejects the three claims that he makes takfir a) on the basis of mere presumption, and absence of certainty, b) on the basis of (the mere absence of) loyalty to himself, and c) of the ignorant person upon whom the proof has not been established (by showing him that he is opposing the deen which the Messenger came with). He explains prior to this statement:

تكفير من بان له أن التوحيد هو دين الله ورسوله، ثم أبغضه ونفّر الناس عنه وجاهد من صدق الرسول فيه،

Which means that takfir is made after it becomes clear to a person that this Tawhid is the deen that Muhammad (sallallaahu alayhi wasallam) came with, then hated it, and drove people away from it, and fights against those who believed Muhammad (sallallaahu alayhi wasallam) regarding it.