This is a well-established store among those who are in the know.
この場合、次のような言い方ができますよ。
ーThis is a well-established store among those who are in the know.
「ここは知る人ぞ知る名店です」
a well-established store で「名店」
among those who are in the know で「知る人ぞ知る」を表現できます。
ご参考まで！
カナダ 
