Passage Summary: The author assumes that because health store employees make more money by selling certain vitamins, everything they say about those vitamins must be a lie.

Conclusion: You can be certain that the claims made by health store salespeople regarding product quality are false.

Reasoning: Salespeople are incentivized by commissions to push specific products, and all major health store employees work on a commission basis.

Analysis: This argument suffers from a 'motive implies falsehood' flaw, which is a variation of an ad hominem attack. The author correctly identifies a potential bias (commissions), but then leaps to the extreme conclusion that this bias guarantees the information provided is inaccurate. In reality, a salesperson might push a high-commission product that actually is the best one on the shelf. Look for an answer that points out the argument fails to consider that a biased person can still tell the truth.