When peer review works correctly, it's hard to tell how it went well.
When peer review isn't used at all, you can tell.
In 2019, literature scholar Naomi Wolf published a book, Outrages: Sex, Censorship, and the Criminalization of Love, with a non-academic press.
Whatever their review process, it was overlooked that the work had a serious flaw: Dr. Wolf misinterpreted the British legal term "Death Recorded" to mean a death sentence -- it in fact meant a pardon or commuted sentence. Worse still, Dr. Wolf was called out on this live on BBC and the book was recalled from bookstores.
![Example of when peer review doesn't take place; Dr Wolf's book is cancelled because it wasn't sufficiently fact checked](https://libapps.s3.amazonaws.com/accounts/323887/images/BBC_article_on_Wolf_Book.png)