My father is a used bookdealer and one of his sources of inventory on occasion has been library discards. (Books with library markings that are sold online ought to be marked "ex-library", not just "used", so that the buyer isn't surprised by this.)

But it's amazing to see this level of automation and scale. My father was manually cataloguing everything and then selling ex-library books for at least a few dollars apiece (often more based on rarity). The dealers profiled here are able to do this on a scale orders of magnitude larger, and cheaper, than a small-scale bookdealer could do by hand -- at least without barcodes.

The barcodes, as mentioned in the article, are a huge deal in that they can change some kinds of cataloguing from minutes of labor to seconds of labor. But ISBNs themselves were only invented in the early 1970s and bar codes on books weren't common until the 1980s. Depending on what decade the books you're dealing with are from, the level of automation of cataloguing could also vary quite a lot.

One thing you'll also see (which antagonized my father quite a bit as a dealer but which can definitely be seen as a huge boon for readers) is that individual people will go to huge sales, like library sales, at the earliest possible moment with phone apps and try to scan thousands of books to find those that will sell at enough of a premium above the sale price to be worth buying. Traditional dealers with brick-and-mortar shops and/or specialized knowledge of some area have some rather negative terms for these competitors, who notably may not have a lot of personal knowledge of the books they're reselling, but do have a lot of dexterity and access to big online databases.

In general, online databases and subsequently mobile apps have done a lot to make the used book market much more competitive, and also much more accessible for smaller-scale participation by non-experts. That's often a hard thing for used book shops and a useful thing for readers.

Library discards or "deaccessionment" are still a sad thing to me, and I think to most librarians too, although they'll often point out that many volumes that are being deaccessioned haven't been checked out in years. A good thing for preservation is that the Internet Archive now acquires a lot of these volumes in various ways and scans them with the goal of getting them online.

There are absolutely books still being thrown in the trash all the time that would be worth hundreds or thousands of dollars to the right buyer, but they're also an incredibly tiny fraction of the books that are thrown away.

> how many books are "lost" because of some scanning fault

Scanning processes are getting better and better, so I also think this is a diminishing problem.

Nicholson Baker wrote a fascinating book called Double Fold in which he pointed out that paper books are typically much more durable than many people think¹, and that digitization and imaging projects have significant drawbacks and limitations. Librarians were quite annoyed with this book because it attacked them as negligent stewards of history. I don't think Baker's arguments have aged very well, as current scanning options are much better and have produced much more useful results than many of those he attacked.

¹ This is true -- Baker points out that our intuitions about fragile paper are mostly shaped by a few decades in the 20th century in which the use of high-acid paper became common for cheap mass-market books, and also for newspapers and magazines. Most older books were printed on lower-acid paper which often lasts for many centuries without major degradation. I have a number of books from the 1700s that are still in great shape and can be read by hand without damaging them (though most have been rebound, because the bindings are normally more fragile than the pages).