You can’t put a carry or service in the window. It is not a tangeble thing. It is an agreement between players.
You can put a stack of cloth in the window and gold in the other window. That is supported. You can even put a stack of mats in the window and gold along with in-game text agreement to craft X. That can be reported and recovered.
Services and loans though, are not supported and never have been.
If Blizz wants to support such services they would make a board where you list your service, a person pays, and if you don’t complete the service the gold is refunded and a negative mark is set against them. All auto tracked.
That opens up the whole “is boosting, carries, etc even good for the game?”