(Author note -- I am trying to do more blogging and less long Twitter threads.)
Recently I had a very respectful conversation with someone who bought one of my books (The PHPUnit Cookbook) and is not happy with the book. They have pointed out the things they don't like and believe are wrong, and finished off one email with the phrase "sorry if I am coming across as harsh".
In my response I did say that I am not offended by feedback. Some feedback is helpful. Some is not. All I can control is how I choose to react to that feedback. Like my mother taught me: we're not losers, we're choosers.
I did finish off the conversation by pointing out that LeanPub offers a money-back guarantee on all their books. I am not offended by anyone taking LeanPub up on that offer. I would prefer to have happy customers rather than ones who felt they wasted their money on one of my books.
Maybe that book just isn't a good fit for them.