2 I have included a spoiler in order to hide the answer for those who attempt at solving the puzzle independently.
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Drink 1 was only poisonBecause. Drinks 2+ also contained the antidote. Who's the better (repeat) customer?.

...Drink 1 was only poison, and Drinks 2+ also contained the antidote. Who is the better (repeat) customer?

Drink 1 was only poison. Drinks 2+ also contained the antidote. Who's the better (repeat) customer?

Because...

...Drink 1 was only poison, and Drinks 2+ also contained the antidote. Who is the better (repeat) customer?

1
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Drink 1 was only poison. Drinks 2+ also contained the antidote. Who's the better (repeat) customer?