https://www.libraryextension.com/ is a browser extension which tells you if a book you're browsing on Amazon is available in your local library.
What an amazing idea! (I've just submitted a request to have my local library added.)
Yes bookfinder.com is great. For French books I also like https://www.chasse-aux-livres.fr/ which also search in some local french websites for used books.
I was about to recommend it. The UI is lackluster but it doesa great job at collecting sources and taking both currency conversion and shipping into account.
It’s my go to. It handles currencies and location for shipping very well.
It’s also an “old school” website that’s very very fast with minimal js. Love it.