More Words, Deeper Hole

Is there an ethical difference between "pay for an ad to appear on some book-focused blogs" and "pay someone to write a blog post singing the praises of my book?" (Presuming, of course, that the book is praiseworthy in the first place. Not talking about upgrading an evaluation--just being willing to evaluate this book, instead of the thousands of others coming out this month.)

I would think the obvious ethical difference is that the ad is demarcated from the text.

Advertising is about identifying or creating an insecurity and offering to address it in a way that makes a profit for the advertiser. (The route to the profit can be mistaken or long, but that's the category.) Everyone targeted by advertising at least has the opportunity to recognize that it is not undertaken in their best interest.

Were one to pay for reviews to appear on a book-focused blog, the readers of that blog doesn't necessarily know it's an ad; indeed, I'd expect that business model depends on the reader not knowing it's an ad. The reader needs to think it's a review. (An ad wants you to buy the book; the review wants you-as-a-reader to recognize the reviewer as consistent and useful. These really aren't the same objective.) If they think it's a review, they're being misled.

That potential -- nigh-certainty -- of active deception is I think the ethical difference.