"… negative or unkind fictitious reviewers were seen as less likeable but more intelligent, competent and expert than those who expressed the the same messages in gentler ways."In other words, when writing book reviews, there may be some payoffs for being an asshole! Being flip, clever, or sharp in your review carries a secondary gain in creating an image that you are more intelligent.
As a matter of fact, this can also pay off in terms of the job market. In magazines with book (or movie) reviews, readers pay more attention to clever, entertaining reviews. And publishers will see this as increasing sales, in the long run.
There's one problem: If too many reviewers follow this ploy, then their acidic reviews do not stand out as much in relationship to the others. The contrast effect is muted.