Believing an article about financial investments because the author has a PH.D. in economics.
Which one is the best answer?
a. is the account biased or neutral?
b. What details are included, and what details are left out?
c. How is the author involed in the events discussed?
d. How does the author of the events discussed?
I moved your question to the "Reference" section as you are asking on whether a source is to be valid on the grounds of their preparation,and there is no other tag than Reference for it.
OK- It seems that you are asking why should we trust a source based on his or her educational level. The answer is A, but you have to consider B and this is why:
Surely a Ph.D (I am one myself) has learned about biased research, and knows about limitations, validity, and much more when it comes to investigation.
Because of this, I tend to lean to A, since (regardless of the source) you have to ensure that whatever educational level is at stake, the source MUST remain objective and impartial.
I also mentioned B because it is a continuum of A: If you are partial you will tend to leave out info. So, ensure that your source (whatever degree they have) is objective and focused. So, I will stick to A, and watch out for B.