Error messages are one of the items on my mental code review checklist that gets very often excersized, since going from terrible to OK is usually pretty easy,

Error messages are one of the items on my mental code review checklist that gets very often excersized, since going from terrible to OK is usually pretty easy, but it's often a very different mindset from the actual programming task that introduced that error pathway. So usually it's up to the reviewer to notice and guide the author to that improvement.