I understand the point you're making - but let me propose another way of thinking about it: Amazon pays a referral fee regardless of what item is purchased. Whether you buy that book or Goodnight Moon or the Kardashian Family Coloring book, a referral link will pay.

So I actually don't think this creates a conflict of interest regarding this book at all. Why would a "conflicted reviewer" point you toward this book vs any other book that he could be equally compensated for?

The conflict arises in two cases -- if the OP insists you should buy this book that's only available on Amazon vs another book that's widely available. Or if this book happens to be significantly more expensive (and hence pays the OP better) than other books.

I don't think either of those is the case here, so I think your dismissal is perhaps unfounded.