Are there situations where taking an honorarium for trying a textbook on a class is acceptable behavior? A publisher for an e-textbook is offering me an honorarium if I try it with a class. My  own ethical take on this is that I would not entertain this regardless of the size of the honorarium (which I don't know).  I certainly wouldn't do this without full disclosure to the students who I'm forcing to buy the book.  I also don't see this as a particularly good text for my course.

While my own position is sort of steadfast, it's something that I haven't seen before in academic publishing, so I'll ask "Are there situations where taking an honorarium for trying a textbook on a class is acceptable behavior?"
I think if you'd not seriously consider the text without the honorarium, that clinches a "don't do it". That is, external monetary motivations should not be allowed to color your professional judgement. And, given that the appearance of impropriety is itself a potential problem, even if the text is plausible, better to be able to later claim objectivity by not taking an honorarium/bribe...