Many of the books on that site are pirated reprints. Great way to get cheap textbooks, but it's not surprising that they would attempt to ban some of the countries often responsible for those.
Obviously textbooks get expensive, but the thing that makes textbook counterfeiting especially successful is that most consumers who get cheap counterfeits don't care. The content is usually the same and it's not a status symbol like an authentic Gucci bag. So as a consumer, there's really not much difference to you, especially if you got the book for cheap.
Typically, counterfeits are lower quality, but someone who works in the industry once told me that he's seen counterfeits with higher quality printing than the originals, which makes the real books look like fakes!
To me the greater issue is the highway robbery that is college textbooks. A lot of professors force the newest and don't care that a single one costs several hundred dollars, nevermind if the material is literally centuries old (e.g. calculus). If textbooks were a reasonable price, the counterfeit effect wouldn't hhappen.
If the content is the same, in what sense is the book a "counterfeit"? That's just a copy of the book.
People are more worried about taking money that isn't identical to money that came from the mint. By definition, if it's identical to minted money, there is no way to tell that it isn't minted money.
If I stole a money printing press and began producing $100 bills on my own, I would be counterfeiting money. Even with the very same equipment that the Mint would have otherwise used to make the notes. Same atoms and same outcome, but not authorized.
It’s the same with handbags or books.
https://booksrun.com/page/on-counterfeit-textbooks
International editions aren't really a "problem" because they are legal, pirated books are not.
You can buy some otherwise insanely expensive computer books for < $10 because they're Bangladesh editions.
https://en.wikipedia.org/wiki/Kirtsaeng_v._John_Wiley_%26_So....
>Kirtsaeng v. John Wiley & Sons, Inc., 568 U.S. 519 (2013),[1] is a United States Supreme Court copyright decision in which the Court held, 6-3, that the first-sale doctrine applies to copies of copyrighted works lawfully made abroad.