I've just tonight caught an actual citation for gong-farmer.

"Harry King's men took away everything. You saw their carts everywhere. Every rag-and-bone man and rubbish picker, every dunnikin diver, every gongfermor, every scrap-metal merchant ... you worked for Harry King, they said, because a broken leg was bad for business, and Harry King was all about business."
- Terry Pratchett, Making Money (2007)