I’ve also noticed that publishers try to sabotage the used book market: 1) make small changes and publish new editions frequently. 2) provide “online” account

I’ve also noticed that publishers try to sabotage the used book market: 1) make small changes and publish new editions frequently. 2) provide “online” accounts (for answer keys, extra chapters, etc.) that can be signed up for with a key provided with the book. 3) publishing large books as thick stacks of loose pages three hole punched for binders. Without a proper binding these books will soon be worthless, even on the used book market.