This happened over a week ago, but it popped up in my GR feed today; thought I'd share.
It appears that GR user Jacquelyn received a review copy of Jourdan Cameron's Me Squared / Me² and ended up giving the book a one star rating with her review. That didn't sit well with Jourdan's sister Kassie (aka Kassidy Cameron, the book's cover artist), who decided that her brother's book couldn't possibly deserve a "cruel" and "dishonest" rating like Jacquelyn's and proceeded to "explain" (read: lie) that "the goodreads rating system is not based on taste. It's based on execution" and attempt to "teach" Jacquelyn how to properly rate books.
For anyone who can't or won't visit GR, here's a screenshot of the exchange.