One afternoon last summer, I walked into a gun shop, spotted a rifle I liked, and paid asking price for it — no checking the competition on a smartphone. The rifle just wasn’t available elsewhere. Secondhand, it bore light field scars, but also the machining and handwork of another time. I can’t say what the shop’s proprietor got from that sale, only that it was what he wanted.

If you’re counting fewer customers these days and the faithful stop by less frequently, you...