Lying about the quality of someone's writing seems like a very bad idea for a few reasons. In our current age of the internet, a reader wouldn't have much trouble finding the sample pages of a particular book online and reading them. Any lies about someone's quality of writing should be easy to disprove by simply reading the work itself.
Beyond that, negative criticism of creative endeavors often has the effect of drawing more attention to said work. This means that not only will people find their narratives to be based falsehood, it will also cause the author to become more popular in the long run. When one is told that a work is of low quality, their expectations will be much lower if they ever decide check out the work for themselves.
So not only will readers be pleasantly surprised at how good the book is, despite what they've been told, they will also grow a fondness for it greater than they would have otherwise. This all goes to show how foolish it is to spin lies about the quality of another's creative works, or even just for life in general. As Gabe Newell of Valve once said: