What could be more natural?
I assumed that anyone at the annual “friends of the library” used book sale was interested in books. And that they wouldn't mind talking about titles and authors, including other writers in genres that seemed to interest them.
So when I saw someone carrying a couple books by Dan Brown, I assumed they might like international thillers with a note of historical conspiracy So I asked if they were familiar with the novels of Steve Berry, and I pointed to a few titles on a nearby table.
As a compulsive reader, I'm always looking for authors who've written with style in my favorite subgenres. So I assumed anybody toting a stack of hardcovers at a used book sale would feel the same. In at least one case I was right, and I shared suggestions about a few authors, and received ideas in return.
I asked someone with three hardcover Dirk Pitt adventure novels by Clive Cussler, if she knew about the author's nearby museum, where he keeps the classic autos that make cameo appearances in the stories. She didn't know, and seemed pleased to hear about it.
When I took my bagful of books to the checkout area, I noticed a guy with two boxes of fantasy and sci-fi titles. I mentioned I hadn't seen any, and he pointed me to where I had overlooked them (on the far end of the table with romances novels). I went back and found two hardcover first printings by an author I collect. Except for his help, I would have missed those.
I realize that many dedicated readers are shy introverts. But we all aren't. The next time you're in a bookstore, don't be surprised if someone comments on the book you're holding. And if you opt not to answer or say much, I hope that person also understands. When someone is carrying a piece of media, it's just natural for some of us to try to be social.