Are these "500,000 books" the same out-of-copyright crap they 9and everyone else) promote elsewhere? Because that's not going to be very interesting to brick-and-mortar bookstores. Nobody's going to make any money on those hundred-year-old books. Bear in mind that for every "Life On the Mississippi" or "Emma" there are a thousand "General Pinklebottom's Wanderings In The Desert, 1811-1812".
(I'm a fan of bookstores myself.)