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I'm not sure what you're getting at here. An endorsement is, essentially, telling people to buy something. All I have done is provided a link to the product here, and a brief reflection.

Would it be better if I included the links without the affiliate tag (e.g. violating ethics by not disclosing a financial incentive)? What if I just didn't even include links to begin with, forcing people who were interested in the book to find it on their own? You could argue that the latter case is a trivial inconvenience (after all, I heard about the book by reading an article that didn't lead to it), but there are systems in place with some marketplaces to reward people for driving traffic. All I would be doing is, in essence, the same thing without actually getting credit for it.

You can argue that the system's wrong, but I think I fall pretty conservative on the ethics side regarding what people generally consider acceptable. I include disclaimers whenever I post a link, not buried down at the end of a post, and I've never endorsed anything I don't believe in. Even when I tear into something, I link to it the same way (with a disclosure), and I don't typically make an outright recommendation to buy something: even when I like something I will only rarely say "You should go check this out" in an explicit manner.

I'm not trying to do a hard sell by any means.