Frankly, I've been wanting to post something about this subject myself for a long time, but wasn't sure how to bring the topic up. It can be sensitive, from an author's POV. But when an agent discusses it, it's more objective. And I'm glad Miriam brought it up, because I think it's something that affects writers at least once in a while.
Here's the link, and here's the comment I left on the thread.
I don’t know if this falls under the catogory of jealousy. But I absolutely despise it when I see online book reviewers promoting certain authors…with an agenda. I’m not talking about giving great book reviews. I’m talking about passive aggressive promotion that most readers don’t notice.
You don’t see it often. But when you do it shouts bad ethics and lack of quality. And it’s not fair to other authors or to readers.