Some years ago, I bought a copy of Stephani et al's book "Exact Solutions of Einstein's Field Equations" from Cambridge University Press. It's pretty much an encyclopedia of all that's known about Einstein's Field Equations. It's the type of book you turn to for advice when you've got a problem, not a textbook you read front to back. So I hope you'll forgive me when I say it took me a few months to notice that the copy I bought was a misprint with several empty pages towards the middle. These are the obscurer parts of the book whose physical applications are at least to me somewhat unclear, and I thought I would just never need whatever should have been printed on these pages anyway.
Over the years however I developed the distinct paranoia that whenever I was looking for something that I could not find in Stephani's book, it was certainly printed on the missing pages. Some time last week, frustrated by yet another intractable set of equations one gets without a good ansatz for the metric, I wrote to Cambridge University Press customer service, complaining about the misprint, with the above photo attached.
Needless to say, several years after purchasing the book I don't have a receipt. Nevertheless, I got a reply within 24 hours, with an apology for the misprint. Alas, the hardcover version that I have is out of print, if a paperback would be okay. "Sure", I wrote back. They asked for my shipping address and a week later I have a brand new copy, all for free. Now if I don't find an answer to a problem I was looking for, I have no empty pages to blame any more.