Here's what Kari said about authenticity:
So just playing the devil's advocate a bit:
Yes, first you have to write a great book. BUT...if authenticity isn't a selling point, why does my publisher lean into my rodeo/ranching background in their marketing for my western romances? And my agent always mentions it when discussing my books (SHE REALLY DOES THIS STUFF.) And readers continually comment on the fact that they love the depth I bring to the page, knowing that I know what I'm talking about. As a reader, I like to see that an author has personal experience in their subject matter because I can trust (hopefully) that what I learn from them is accurate, and I can nearly always see it in the richness of the world they build (again, assuming excellent writing). For those reasons, if I were an agent I would like to see a single sentence about Opie's background in a query because if I love this book, it tells me the author has a deep well of experience to draw from for future work, and a unique selling point that might tip them over the edge with a publisher who's trying to decide between this book and that one, because marketing often rules the day.
The key word here is marketing. Your publisher uses your background as grist for the publicity mills. A writer who actually ropes? Yowza, send photos at once!
This helps the publisher hook the media's interest in the books. As you might imagine, I'm all in favor of that, BUT it's not something I consider at the query stage.
At the query stage, what I care about is story. The book Kari originally queried involved a thief. I didn't ask if she'd actually done time. Nope, I read the book, fell in love with the writing, and THEN starting thinking about marketing.
The flip side of authenticity though is that often someone who really knows a field has a hard time writing outside the facts. I see this a lot with lawyers, doctors, and law enforcement who query me about books that "don't take liberties with the facts!" and are thus often short on plot.
Reality is very rarely a good story. That's why we have you: to take liberties with reality and give us a good tale.
It helps if you've lived in the world I suppose, but honestly, despite all his efforts Colin Smith has not actually been to Carkoon, yet I believe every word he writes about the kale fields there. Lee Child didn't serve in the US Army; Michael Connelly isn't a cop; and last I checked David Simon is not a drug dealer (although I am addicted to The Wire.)
Bottom line: I never reject a query based on what an author says about their background (exceptions: cannibalism; shark soup chef; Nazi) so if you include it, it's not a problem. BUT if you are writing about cowgirls, and your only rodeo experience is the Seventh Avenue IRT, I'll still read your story if it sounds interesting.