knocker

on the knocker informal 非正式

(Brit.)going from door to door canvassing, buying, or selling

(英)挨家挨户地盘查（收购，卖货）

(Austral./NZ)(of payment) immediately; on demand

(澳／新西兰)（支付）立即；在要求时

he has to pay cash on the knocker.

他必须立即支付现金。