Gold Dupe - Requires Automation (Patreon)

The Alliance-only quest "The Eye Of Paleth"in the Wetlands gives you a quest item, which, unusually, is equipable and vendorable. You can simply keep selling the item and abandoning the quest from the chest which starts the quest. You will need some means of breathing under water as that is where the quest is.

The quest chain leading to this one begins with "The Third Fleet" which can be picked up in Menethil harbour from First Mate Fitzsimmons, who is outside the inn. 

The item sells for 2 gold and 98 silver currently so to make this worthwhile you probably need some form of automation. The dupe has been known for a while but the value of the item just increased by a factor of 10 making it much more interesting.

If you do not have an alliance character, then a class trial alliance character will do, it takes only minutes to set up. 

It is 2;20 am as I write this, I'll try and contribute more on this tomorrow though I made commitments elsewhere (foolishly thinking the day before the new xpac was the one day I could take off safely:)). 

EDIT: The mammoth vendor method we usually use this for sort of dupe isn't particulary effective here, as Daniel kindly points in a video he links to below, the mammoth can't be mounted in the confined space. An alternative method is to accept the quest, destroy the eye, abandon quest, repeat. The eyes can then all be sent to your mailbox by the item restoration process. This may (speculative) somewhat confuse Blizzard also.