"She's a maven of the history of the synagogue."

"They think they're a maven in medicine because they live next door to a doctor."

"'I’m a maven, as my family used to say,' she said. (She also describes herself as a nice Jewish girl from Long Island: Lawrence High School, class of 1983.)" (source)

“Don’t buy it until you get the advice of a maven." (NJY)

"If you want to know the best buy in amplifiers, ask my brother-in-law—he's a real meyven." (Glinert)