Learn Farsi: بر اساس درجه‌بندی جدید، این الماس را بی‌بها می‌پندارند. - According to the new grading, they consider this diamond worthless.

This is the core predicative complement structure you are learning. Verbs of consideration like پنداشتن (to suppose or consider) take a direct object marked by را (here, این الماس را), followed immediately by a bare adjective or noun (here, بی‌بها). Farsi does not use a linking word like 'as' or 'to be' in this structure; you simply place the complement right before the verb.

The translation says 'they consider', but couldn't we use می‌دانند here instead of می‌پندارند?

Yes, می‌دانند (from دانستن) is a very common way to express 'they consider' and would work perfectly here. The verb used here, پنداشتن (present stem: پندار), also means 'to consider', 'to suppose', or 'to imagine'. It sounds a bit more literary or formal than دانستن, but it follows the exact same grammatical structure for its complement.

Who exactly is the subject of می‌پندارند if nobody is mentioned earlier in the sentence?

The sentence uses the third-person plural ending -اند to create an impersonal 'they', much like we say 'they say' or 'they consider' in English to refer to experts, authorities, or people in general. In Farsi, this is a very common and natural way to express a passive idea without actually using a formal passive verb construction.

How is the word درجه‌بندی (grading) formed?