Setting: Lunch yesterday at Chez Albert in Amherst, a small, cute, dark French restaurant. I am seated in the window, with a professor of French Literature who I’ll leave anonymous. We’ve had eggplant Napoleons and are finishing up.
French Lit Professor: Just as long as you don’t do something like, well, I mean the mistakes people make when they write about Paris in the 19th Century are just terrible.
Me: Tell me, please. I was going to ask you but then I didn’t. What are the worst ones?
FLP: Well, parties in the Tuileries when it was knocked down, or even people living there when it was still a ruin. There was one novel where they climbed the Eiffel Tower, which hadn’t been built at the time. In another, they got on the Metro, which wasn’t in place until 1909 or something. This isn’t hard to check!
Me: [Blinking in horror at the idea of being one of these people] There’s that beautiful collection of photographs online, through Northwestern University, of the ruined Tuileries.
I’ve gone to Paris to do stage-blocking. I’ve stood where she’d stand, to see what she’d see, and then got a book of postcard photos, with pictures of monuments now, vs. then…
FLP: I have that book! And then, my Lord. There we were in the Louvre, the Louvre! And they were selling that tour, for that. . . the [bestseller title redacted].
[He squints] And that book has a scene where he describes at the beginning going from the Left Bank to the Right Bank and it’s as if it’s reversed. All of the monuments in reverse, right at the beginning. And they have [bestseller title redacted] tours on sale in the Louvre with these mistakes. My wife noticed it first and then I did. I mean. . .Don’t do that.
Me: I’m trying very hard not to.
FLP: If you like, I’ll read the draft and I can tell you where you’re messing up, if I know.
Me: I’d like that. I’d prefer you find the mistakes before rather than after.
Koreanish 
Don’t worry needlessly Alex. Your book will be wonderful and beautifully written, whereas {bestseller title redacted} sucked out loud and was poorly written.
Thanks, Tony— ‘blinking in horror’ was meant to be a little funny. But there’s two things. One, in the experience of myself and other authors I know, there are people out there with knives waiting for you to get just one detail wrong. I’ve had anecdotes from too many friends to disregard the importance of ‘getting it right’, so, while I’m not having anxiety attacks, I’ll be seeing more experts until I’m done.
Two, nothing disappoints someone who wants to like you more than you being ignorant on your topic. A writer giving wrong details, for a reader that’s like going to a restaurant and having bad food.
Though yes, the mistakes didn’t keep [bestseller title redacted] from making a lot of money.
“I’d prefer you find the mistakes before rather than after.”
Isn’t that kind of everything, I mean true of everything?
sigh. I need to go redact some stuff.
The French Revolution was the only thing that ever interested me in my European History class. I think I’ll enjoy your next novel.
I threw a huge party for 200 or so of my closest friends and family, gave out the free stuff and sold the books… got home, sore feet and partied out. Content and proud and all such things.
The next morning, just before local bookstores sold it, and a huge promo thing, I ran a hot bath, took the book into it with me. Read and read and read… and there, on the last page was a glaring, GLARING error. I nearly broke my legs jumping from the tub to the telephone.
Monday morning = reprint.
Fortunately, they’d only done 500 for the weekend. Also best if you own the place.
It was a very good lesson in letting someone else have their hands on it one more time before it goes to press.
As you wrote in your comment, people are nasty and waiting with knives.