One: I don't think using fur as currency would work at all. It would probably be confusing and difficult.
Two: This suggestion seems to go into major-quests, which are obviously very far away.
Three: The whole "is it really worth losing all my alignment with the other Far Harad Factions just to get a bit of alignment with these war driven maniacs" thing is all a bit ridiculous imo.
Let me try and explain why this sounds a bit silly. Let's say you are friends with Isengard, Mordor, Angmar, Gundabad, and Dol Guldur. But, for some reason or other, you join Fangorn. Is it really worth it to lose all your hard-earned alignment just for a bit of Ent-Draught and some Huorns?
Sorry if all this is a bit confusing. I just woke up. But all in all I'm not for this suggestion.
Yeah this is a suggestion for the possible far feature and cause few had written about the Cerinrim.Since they are said to be enemies of all factions in Far Harad I thought of some Side Quest type thing that would make it worth it.And the other stuff was to make them unique and interesting like the Fur Trading mechanic.Also it would make sense like Fangorn as you said.Which does not have silver coin trading Ents for example as that makes no sense.The folk of Cerinrim would likely not trade in silver as they are so far away from any civilizations who trade in that who are not enemies and they likely would not find it useful.Most hunter gatherers society barter with stuff like furs instead of worthless shiny metals.