Some producers of vitamin pills are guilty of
This answer is very tempting. It's softly worded and it feels like an Inference we can pull out of the Premises (however, that's not our goal -- we're supposed to be thinking about Assumptions exist in the move from the the Evidence to the Conclusion). Would it hurt the author if we said, "No producers of vitamin pills are guilty of false advertising?" No, not really. First of all, her argument could be read as purely hypothetical -- she hasn't said anything that commits her to the idea that there actually ARE vitamin brands being advertised as "higher quality / more natural". I could make an argument that says, "You should NOT accept anyone's offer to give you a private ride to the moon" and it could be purely hypothetical. That argument doesn't assume that some people ARE offering private rides to the moon. Furthermore, while the author would say it's false to advertise that one vitamin pill contains higher-quality vitamins, she wouldn't say it's false to say that one vitamin pill has more natural ingredients. In a world where vitamin producers advertised their more expensive vitamins as having "more natural ingredients", our author could say, "They're not false advertising. It does have more natural ingredients. But there's no reason to pay extra money for natural ingredients since natural vitamins and synthesized vitamins are exactly the same."