This has been going on since way before the internet--Texas used to have de facto veto power over public school textbooks, because the Texas Board of Education

This has been going on since way before the internet--Texas used to have de facto veto power over public school textbooks, because the Texas Board of Education (or whatever it was named) was the single largest buyer of textbooks. If you're a big enough buyer, then you start to claim some amount of monopsony power.