> If you order from your local bookstore a book which is being sold on Amazon as a PoD copy by a major publisher, what do you think happens?

Nothing. Local bookstores (not just 'mom-and-pop', but national chains or cooperatives) would tend not to have that title available. Is that a US thing that they would order from Amazon? Printing-on-demand is potentially interesting, but just not a thing for most titles.