There are several commentaries of the Quran by acclaimed Islamic scholars. Can these be accepted completely as authentic? If not, how does one distinguish between what is credible and otherwise in these Tafsir works?
Not all of the commentaries are completely authentic. Many commentaries contain unauthentic narrations or incorrect views or opinions. You need to seek guidance from sincere and knowledgeable scholars before taking any commentary fore granted. You can take the commentaries written by our big scholars according to the authentic narrations from the Prophet (SAWA) and Ahlul Bayt (AS).
Wassalam.