Why would a person trust opinions of another over own judgement?

If you don't know something it does not mean you don't have an opinion, you ask a question and get an answer, we evolve that way, because we can't know eveything. You can form you opinion from the answer you get and it doesn't have to be someone's, because you don't have to agree :). Ironic, that you ask that question, probably sit around and waiting for the answers :))

I wouldn't. Unless I knew the person very well, and knew they had special expertise in the area of the question. Like, my family doctor.

Other than that, I trust myself first.