Herbalist: Many of my customers find that their physical coordination

let us simplify the argument given here --

Premise
1. many customers found that their physical coordination improves after drinking herb juice
2. a few doctors assert that herbs are potentially harmful
3. BUT doctors are always trying to maintain a monopoly over medical therapies

Conclusion
No reason not to try the herb juice

Note that the argument rejects point #2 in the premise by attacking the "source" of the argument and not by attacking the argument itself. This is a classic flaw in reasoning.

Option A - Incorrect

The author does not try to induce "fear of consequences" of his claim. Incorrect.

Option B - Incorrect

None of the three points mentioned in the premise contradict each other. Incorrect

Option C - Correct answer

Correct answer. This answer states that the author establishes his claim by attacking doctors by stating that the doctors are not trustworthy. Hence, the claims they make are also not trustworthy. However, the argument does not evaluate the claim itself.

Option D - Incorrect

this suggests that the argument employs circular reasoning. I.e. Premise = conclusion.
This is not done here.

Option E - Incorrect

One thing happens after the other is not mentioned here.