This will become clear from the following points:
Know well that the Rawafid previously practiced upon the narrations of their scholars without any investigation and research. And there did not exist in them anyone who could differentiate between the various narrators of the Isnad, nor anyone who wrote a book regarding Jarh and Ta’dil. This was until al Kashshi came along in about the fourth century and authored a book regarding Transmitter biographies.
This is the oldest book of the Shia regarding the detailing of the biographies of hadith narrators, for there is no scholar before al Kashshi who authored a book regarding the science of men, which is indicative of their lack of knowledge in this field. And it is not known regarding al Kashshi himself when he passed away. All they have confirmed about him is that he was from the generation of Muhammad ibn Yaqub al Kulayni, the author of al Kafi (d. 329 A.H)
Furthermore, this book of al Kashshi is very brief and vague and it does not contain anything helpful or beneficial. In fact, it only increases the reader in confusion due to him citing therein contradictory reports of impugning and approbation without being able to give preference to one view over another. And the amount of entries found therein are only 520.
Al Najashi says about this book and its author:
ثقة عينا روى عن الضعفاء كثيرا… له كتاب الرجال كثير العلم وفيه أغلاط كثيرة
He is reliable in himself and has narrated excessively from weak people… He has written the book on transmitter biographies which contains much knowledge, but in it there are many mistakes.
Al Najashi states that al Kashshi narrates excessively from weak people and that his book contains many errors despite it being their first book of transmitter biographies. Now if this is the condition of one of their most acclaimed scholars of transmitter-biographies in spite of his book being the oldest and most crucial reference in the science, then what can be said regarding the Shia scholars that followed after him, and what can be said about their books.
Subsequent to Rijal al Kashshi emerged the book of al Najashi which is also very brief. In reality, till now I do not know if there is a credible book which can be relied upon for determining whose narration should be accepted from the narrators of the Shia and whose not. For, as a matter of fact, anyone who produces a narration which supports the Imami Rafidi dogma, his narration is accepted without investigation of his personal condition. This is the complete opposite of the methodology of the Ahlus Sunnah scholars, the giants of this field.
Jafar al Subhani says:
هذه هي الأصول الرجالية الخمسة وأما ما ألف بعدها فقد أخذوا مادة البحث من هذه الكتب وهي كثيرة للغاية
These are the five principle sources of transmitter-biographies. As for the books authored after them, they took the content of their study from these books, and they are a lot.
It should also be remembered that these scholars have completely discarded the mention of the dates of birth, dates of death, and the various generations the narrators belonged to. This is notwithstanding that whoever came after them had to necessarily refer to them, so if this is the condition of the principle sources then obviously the secondary sources will be far worse.
Hence, the deviant ‘Abdullah al Mamaqani, who they dubbed ‘al ‘Allamah al Thani’ (the Second Erudite), referred to these books and others in his work Tanqih al Maqal fi ‘Ilm al Rijal. As for ‘al ‘Allamah al Awwal’ (the First Erudite) he is Ibn al Mutahhar al Hilli whom Ibn Taymiyyah had refuted. And the book Tanqih al Maqal is the largest of books in size and the highest of them in stature.
Likewise, there are other later books which contain within them the principle transmitter biography sources, like al Du’afa’ of Ahmed ibn al Hussain ibn ‘Ubaidullah al Ghada’iri. However, this book has placed most of their scholars in the dock, it has tainted them with lying at times, and with forging and extremism at times, as a result of which they doubted the attribution of this book to its author. But, in spite of that, they still accept his approbation if he happens to approbate a narrator whom they venerate, and they reject his impugning if he happens to impugn someone who does not deserve impugning according to them.
Added to the above are also: Majma’ al Rijal of Zaki al Din al Qahbani, Qamus al Rijal of Muhammad Taqi al Tustari, Jami’ al Ruwat of Muhammad ‘Ali al Ardabili, and Mujam Rijal al Hadith of Abu al Qasim al Khu’i, their contemporary scholar.
These are the books of the Rawafid in the field of Jarh and Ta’dil. There is no doubt that the Rawafid have lesser experience and lesser knowledge than the Ahlus Sunnah in this field. In fact, they are too insignificant to be compared with the Ahlus Sunnah in this science and are dependent upon the Ahlus Sunnah in hadith and its compilations.
Furthermore, these books of the Rawafid are replete with misspellings, distortions and lies. The Grand Ayatollah ‘Ali Khamenei states:
بناء على ما ذكره كثير من خبراء هذا الفن ان نسخ كتاب الفهرست كأكثر الكتب الرجالية القديمة المعتبرة الاخرى مثل كتاب الكشي والنجاشي والبرقي والغضائري قد ابتليت جميعاً بالتحريف والتصحيف ولحقت بها الاضرار الفادحة ولم تصل منها لابناء هذا العصرنسخة صحيحة
Based on what many experts of this field have stated, the manuscripts of the book al Fihrist, are just like the early credible books of transmitter biographies, like the books of al Kashshi, al Najashi, al Barqi, and al Gada’iri in that they all are victims of distortions and misspellings; due to which they bare disastrous harms. And not a single authentic manuscript of them has reached the generation of this time.
What is evidence of this is that al Najashi has, for example, stated in the biography of Muhammad ibn al Hassan ibn Hamzah al Jafari:
مات رحمه الله في يوم السبت سادس شهر رمضان سنة ثلاث وستين وأربع مائة
He passed away, may Allah have mercy on him, on Saturday, the sixth of Ramadan, in the year 463 A.H.
Whereas al Najashi, the author of the book, passed away in 450 A.H. So does it make sense that this narrator passed away thirteen years after the author of the book?
Furthermore, the science of Jarh and Ta’dil of the Rawafid is riddled with contradictions and disparities. Al Fayd al Kashani says:
في الجرح والتعديل وشرائطهما اختلافات وتناقضات واشتباهات لا تكاد ترتفع بما تطمئن إليه النفوس كما لا يخفى على الخبير بها
In Jarh and Ta’dil and their requirements there are disparities, contradictions, and confusions which cannot be alleviated with a solution which is soothing to the heart, as is not unclear to one who is well-informed about them.
And ‘Ali al Khaqani says the following in his Rijal:
اختلف علماؤنا في توثيق كثير من الرجال أو في الأكثر بل في كثير من الأعاظم فترى هذا يوثق محمد بن سنان بل يجعله في أعلى درجات الوثاقة وآخر يضعفه بل يجعله غاليا وكالمفضل بن عمر إلى غير ذلك
Our scholars have differed regarding the approbation of many transmitters, in fact most of them, in fact even regarding many of the greats. Hence, you will see that this scholar approbates Muhammad ibn Sinan and even goes on to consider him to be on the highest degree of reliability, whereas another will deem him weak and even consider him an extremist. And like al Mufaddal ibn ‘Umar and others.
If this proves anything, it proves their lack of expertise and knowledge in this field, and it indicates to the greatness of the Ahlus Sunnah.
 Mukhtasar al Tuhfah, p. 54.
 This is the general style of the transmitter-biography scholars of the Shia. And, by the way, al Kashshi is not the only one who cites conflicting reports regarding one narrator. Also, the difficulty one is confronted with when studying their books of transmitter-biographies is that whenever any criticism is cited regarding a narrator, they have to follow that by averring that it was advanced by way of Taqiyyah, so that he is not doubted by the Muslims.
 Rijal al Najashi, p. 372, under entry no. 1018.
 For an introduction to these books refer to: Buhuth fi Fiqh al Rijal of Hussain Makki al ‘Amili, p. 26-28; Usul ‘Ilm al Rijal bayn al Nazariyyah wa al Tatbiq 1/34, onwards; Durus Mujazah fi ‘Ilmay al Rijal wa al Dirayah, p. 11.
 Durus Mujazah fi ‘Ilmay al Rijal wa al Dirayah, p. 12.
 Al Usul al Arba’ah fi ‘Ilm al Rijal, p. 34.
 Rijal al Najashi, p. 404: entry no. 1070.
 Refer to: Tashih and Tad’if according to the Rawafid, in this book.
 Al Wafi, 1/11, 12.
 Rijal al Khaqani, p. 82.