一道weaken题

YWAC

Books and Coffee
The owners of a book store and a nearby coffee shop have decided to combine their businesses. Both owners believe that this merger will increase the number of customers and therefore the gross revenue, because customers who come for one reason may also decide to purchase something else.
Which of the following, if true, most weakens the owners' conclusion that a merger will increase revenue?
Books and drinks can both be considered impulse purchases; often, they are purchased by customers without forethought.
Profit margins at a coffee shop are generally significantly higher than profit margins at a book store.
People who are able to read the first chapter of a book before buying are more likely to decide to buy the book.
A large majority of the book store's current customer base already frequents the coffee shop.
A combination book store and coffee shop that opened in a neighboring city last year has already earned higher than expected profits.
weaken题一直正确率不高，求大神解题思路。

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