On the one hand, we do things that would set me off screaming if they happened to me as a retail customer, and on the other, I now know why those sonsofbitches at every retail establishment I go to do the things that set me off screaming most every time I try to deal with them. They lie because the truth is complicated and not pleasant. They lie because the truth isn't part of the retail experience.
The truth, when you order a book (or, really, anydamnthing you order at a retail esablishment), is this: We don't know how long it will take. Your book (or whatever) will arrive when it arrives. I've done, within the extremely limited scope available to me, the sum total of what I can do. From here on out, it's up to the gods of Buying and Receipt, and to God, when your book (etc.) gets here, if your book (...) indeed gets here. If the Buying gods see fit, It will be ordered the next time we order from the sources we order from, and it will arrive if they see fit to send it and God sees fit to allow it to arrive, and the gods of Receipt put it into the system and it's not lost, mangled or just plain vaporized by evil magic, then you'll be in a position to get your book (,).
That's the answer, and so we say "I'll order it, and it should be availble in 5 business days or sooner." Because the lie is more "retail" than the truth.
Now You Know.