Finding a book's ISBN for free is easier than most people think, and I’ve spent years digging through resources to nail down the best methods. The go-to move is using library catalogs like WorldCat or the Library of Congress—they’re free and packed with metadata, including ISBNs. Just type the title or author, and bam, there it is. Google Books is another underrated gem. Pop in the title, and if the book’s preview exists, the ISBN usually shows up in the 'About this book' section. It’s like a treasure hunt where the prize is a tiny string of numbers.
For older or obscure titles, I swear by used bookstore sites like AbeBooks or Biblio. They list ISBNs for every edition, even out-of-print ones. Sometimes, the publisher’s website or academic databases like JSTOR (free access through some libraries) include ISBNs in bibliographies. And don’t sleep on Goodreads—their community often fills in missing details, including ISBNs, in the 'Editions' tab. It’s wild how much info is out there if you know where to poke around.