Who is the deceptive narrator (al-rawi al-mudallis), is his narration accepted, and is deception (al-tadlis) not a disparagement of the narrator?

The answer discusses the types of tadlis (deception/concealment) in hadith:

1. Tadlis al-Isnad (Concealment in the Chain of Narration): This is when a narrator transmits from his shaykh something he did not hear directly from him, but rather heard it from another, weaker narrator whom he does not mention. He uses ambiguous expressions that suggest direct hearing, such as "from" ('an) or "he said" (qala). The hadith of a trustworthy mudallis (one who practices tadlis) is accepted if he explicitly states that he heard it directly, using phrases like "he narrated to me" (haddathani) or "he informed me" (akhbarani).

2. Tadlis al-Taswiyah (Concealment by Levelling): This is when a narrator drops a weak shaykh who is situated between two trustworthy narrators in the isnad, making the hadith appear as if it is a chain of trustworthy narrators. This type is considered the most egregious form of tadlis. The hadith of a mudallis who practices this type of tadlis is accepted if he explicitly states the direct transmission (from the dropped narrator).

3. Tadlis al-Shuyukh (Concealment of Shaykhs): This is when a narrator mentions his shaykh by a name or kunya (patronymic) that is not well-known for him, in order to conceal his identity. The intention behind this might be either for a disliked reason (e.g., the shaykh is younger or less famous) or a forbidden reason (e.g., the shaykh is not trustworthy).