If you're ever in my hometown of Portland, OR, USA, be sure to visit Powell's Books. Over 1,000,000 books spread over 68,000sq/ft / 6,300sq/m. Back in the day, they were buying over 3,000 used books/day. COVID has hosed all that, but they still have 64,000+ used books available Online.
Image Source: Conde Nest Traveler
They have a 'Rare Book Room', too.
Image Source: Powell's Books
But, Z, you have Shakespeare and Company and Athena, you have Politeia, among countless others, it would appear. There in Europe you seem to have armies of cozy, little bookshops. Very fun!
This bookstore looks splendid. I would love to go there... And I would dread having it nearby!
In Paris, Shakespeare and Co is a famous bookstore, but mostly for tourists. There are many small rooms fully packed of English books, so it's nice to have a tour there. But there is very little to no second-hand offerings, the prices are not so good, and whenever I went there to find a very specific title, they didn't have it.
The true "big" one is Gibert Joseph. It's a giant five-stories bookstore, with both new books and second-hand books (and the latter get increasingly fewer as years go by). That's where I went for my lunch loot. When I was a kid, each time we went to Paris with my parents, my dad would go there for a while. It was actually fairly boring as he spent way too much time to our taste and we didn't even get books.
Now this is a bit sad, but in the same street, there used to be an other bookstore called Gibert Jeune. It was actually a network of one big four stories book store and a few more small ones, all located within a hundred meters radius. These were the two major second-hand bookstores of Paris. But Gibert Jeune suffered a bit, and Gibert Joseph bought it. Except they sold it soon after that and during the last lockdown, these historical "Gibert Jeune" bookstores came to a close.
There was even a third (!) giant bookstore in that same street called Boulinier. This one was smaller, only three stories, and was quite a mess to be honest. But the prices were extremely low. So you would go there, spend some slice of time, and hope to find a good deal. I seldom left empty-handed! This one also closed two years ago.
Unfortunately, in Paris, each square meter is so expensive that bookstores close one after the other to be replaced with more profitable shops.