If you don't like it, change it
Technically, there is no review mechanism to detect whether an instructor introduces errors or adds material that the author whose name is on the cover would find unacceptable. The system is completely under the control of the individual instructor.
Were there a wiki-based approach that allowed a community of similarly situated instructors to revise and improve the text, with the author being able to accept or reject such changes, this would be a way to keep scientific texts, for example, up to date with the latest research. But under the system as Macmillan has designed it, students will soon be subjected to freshman biology texts that replace the Theory of Evolution with Intelligent Design or some such.
This is more than a bad idea (and thanks to Brian Akers for bringing it to my attention). This represents a total abdication of any duty on Macmillan’s part to control the quality of the books they publish. But this is not an entirely new phenomenon. Ever since publishers started to be acquired by conglomerates in, what, the 1980s?, MBAization of their management has turned them away from any sense of social or cultural responsibility. This is just one more (and one very disturbing) step in that process.