JACK BERNSTEIN walks into the Melrose Trading Post, a Sunday flea market at Fairfax High School in Los Angeles, and stops before five seconds have passed. There is a vintage sunglass peddler with a stall near the entrance, and Bernstein is scanning the inventory for high-end vintage sunglasses faster than a quality-control specialist on a Jelly Belly assembly line. “These are Persols from the 1980s,” Bernstein tells me, referring to the luxury Italian eyewear brand, as he picks up the pair.