I don't understand why you couldn't just put a book upside down on the shelf if you want its spine print to face the same way as books that are printed the other way around. "Don't worry, the letters won't fall out."
Likewise, if it's so important that the spines can be read for a stack of books in a store, turn all of them to their face except for the top one... oh, yes, and hope that no-one buys the top one or else someone needs to keep flipping the new top of the stack.
I'd wager that many people (such as me) think it feels "wrong" when the book is upside down. This is especially true if the spine has some sort of artwork.
At high school and uni whenever I carved my name with pen into the page edges of my newly bought textbooks on the first day of term to dissuade book thiefs, I always held the book face up while doing so. It would have felt unnatural to hold the book upside down while performing this sacred rite.
Likewise, if it's so important that the spines can be read for a stack of books in a store, turn all of them to their face except for the top one... oh, yes, and hope that no-one buys the top one or else someone needs to keep flipping the new top of the stack.