This is dupe going back to ~2004 and is still in game. It allows certain items to be duplicated, typically items that bring up some sort of confirmation window before they're used.
I'll use a 30k resource kit as an example. Do the following:
Set up a vendor.
Put your kit up for sale.
Leave the kit for sale for (to be safe) at least 30 minutes.
Cancel the sale and retrieve item from the stock room.
Use the kit, ie bring up the resource selection window (DO NOT choose a resource yet)
Leave the window open and put the kit back up for sale.
Now select and take the resource you want.
The server will attempt to destroy the kit, when this happens the kit sale will automatically cancel and the kit will end up in the stock room.
Now you can repeat the process of retrieving the kit, use the kit and bring up the selection window, put kit back up for sale, choose a resource, the kit sale cancels.
Important thing to remember once you start this use process you only have a few minutes to repeatedly use the item, after that it will be destroyed. All you're doing is temporarily delaying its destruction.
You could use this process for duping anti-decay kits back in the day. Now its uses are limited, last time I used it was for duping legacy dna.
Enjoy it while it still works/till the game ends