expression
no first-time customers; regulars only
A policy phrase used by some traditional restaurants, bars, or establishments that refuse service to customers without an introduction or prior relationship. Often seen on signs or stated as a rule.
その料亭は一見さんお断りなので、常連の紹介が必要だ。
That traditional restaurant has a 'no first-time customers' policy, so you need an introduction from a regular.
From 一見 (first-time visitor) + さん (honorific) + お断り (refusal). The exact historical origin is uncertain, but the phrase is associated with traditional hospitality practices where trust and reputation are built through personal introductions.