"What difference does it make who is speaking?"

I was trying to answer for myself this last question with which Focault left us. As someone who is being judged (and sometimes even graded :) ) based on what they say or write, I think it makes a big difference who is speaking. Especially in the modern world, where we hear/read/see so much information, we need to know who is behind those words in order to decide (that doesn't necessarily mean that we will make the right decision) whether to believe the statement or not. I'm much more likely to trust my physician than someone with no medical education about questions concerning my health. Of course, the fact that my physician told me something doesn't make it true (and I've regretted my trust many times) but it's the probability of it being true that keeps me following her advice. This applies more to everyday facts and science than to art. It's harder to qualify art as "true" and "false", or trustable and not. Also, if it makes no difference who is speaking, what is the difference between any two people? I feel like Focault took his theory a little bit too far ignoring things like education, character and individuality.