High praise not deserved

I occasionally review books, and sometimes they come with endorsements from famous economists. Most of the time those endorsements are deserved, but every once in a while a book that is mediocre at best, or something that never should have been published at worst, arrives with a dusk jacket full of glowing words of praise from well-known economists. I am reading on such a book now. Obviously none of the big-name economists who recommended it had read it--the target audience of the book was not professional economists. So why did they endorse it? Do they not worry that actions like this might reduce their credibility? Or is credibility of economists based only on research ability, so that a string of poorly-advised endorsements does not harm?

I suspect that the reason that this book got the undeserved praise is that the endorsers either know the author or want to be nice to the publisher. One thing that bothers me about this is that it tilts the playing field toward those who already have arrived and makes it more difficult for talented but unconnected authors to break through. I have read excellent books by little-known authors--not a lot, but they do exist. I have also read a number of forgettable books by authors with reputations.