If they don't they shouldn't be working there.
If they do they'd probably be happier working in a library.
I'm assuming most consumers would use their commonsense when going into a bookstore and not search for a Bible in the fiction section.
Common sense is not the same as knowlege of the Dewey Decimal system. Common sense would be to go to the store and tell them to change the label to "Theology" or "Faith".
How would you like it if I tried to force a Muslim or an atheist to read the Bible?
Nobody's forcing you to. The question was, why wouldn't you voluntarily read it just for the knowlege? Are you afraid it will convert you? Don't you want to know what's motivating your enemy?
I have, along with the Baghavad Ghit, Buddhavacana texts, the Book of Mormon, Christian Apocrypha, Gnostic Scriptures, etc., and it didn't hurt my core principals one bit.
The Koran is kind of annoying the way they organized it according to size of chapters rather than chronologically, but otherwise its got some interesting stuff in there. It goes into a lot more detail about the life of Mary, mother of Jesus, than you find in the Bible, and it points to the homeland of the Queen of Sheba, which archeologists have checked out, and turns out it might be right.
In terms of codes of conduct, it's so much like the Bible than the main problem is you'll feel like you've heard it all before, so bring lots of coffee.
In any case, if the way Costco labels the Bible bugs you that much, then what you do is recruit allies.
Specifically, you buy some Korans, stick copies of the "Fiction" label on them, toss them into the bin, then call the local Mosque and give them an anonymous tip, and stand back to watch the fur fly.
At some point you can step in and suggest to management they change the labeling to "Theology" or "Faith", and with that little bit of peacemaking you get to be called a child of God.