First off you have to do a quest which gives an adena prize and it must be repeatable(a quest where you fight monsters and get specific items from them to give to npc)
Then you get a lot of those items and not just enough of the item to just finish the quest but a lot of the items
Now to make this dupe work the NPC server must be lagged or else it just wont work (sooo all you have to do is just make the server lag by dropping 1 adena all over the place but i don’t dink you wanna do that or just spam the message boards or anything else you can think of).
When you finally get the message taht the server will be going down in whatever amount of time rush back to the npc with the quest items you have obtained and then wait for server to restart back up.
Now when you get back ingame the NPC server will be lagged like it always is after server goes down so just talk to your NPC and finish your quest and when you talk to your NPC and finish your quest you get your adena BUT you still have your items in your inventory because the NPC server is lagged.
So just keep on talking to the NPC you got the quest from and keep on finishing the quest over and over and over until the NPC server unlags because when it unlags your items will be gone from your inventory if you finish the quest when the NPC server is unlagged
Thus everytime the server goes down you can use this dupe to get a good amount of adena for yourself Very Happy