Subject-Verb agreement

Neither of the candidates were/was satisfactory.
Neither Raman or David are/is going to do this job.
I don’t think either of them knows/know the truth.
Please guide me.

  1. Niether of the candidates was satisfactory.

Because “niether” is here subject.

Like: The cost of new cars is high.

Just, mind it, after the preposition single subject word never be counted.

  1. Niether—nor

after ‘or’ you must use singular verb.

And the last one, you can understand easily.