Came back to this game a few days ago after quitting during 7.0. Decided to go do some transmog farming as I have no gold, only to find that trash mob loot has been severely reduced. Im talking a full uldaman run with literally only 2 greens from the end chest (which is guaranteed to have greens.) What the fuck is going on here? Also why are bosses dropping the same item so often? Also tried RFK and DM to find the same low drop rates. Any insight is appreciated.
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If you already have a high level character or a friend willing to give you gold then you can purchase Heirloom items. These items are bound to account and are accessible through the Heirlooms tab using Shift+P. The benefits of these Heirloom items is that they scale with your level keeping your gear up to date without you having to worry about upgrades, and they provide a significant XP bonus.
Alchemy is a great profession for gold-making as the main outputs are consumed on use, this means that there will always be demand for new potions and flasks. The old world recipes are also very profitable. Sadly I don’t have Legion alchemy so I can’t personally help you. The best guide I was able to find on the internet is this video guide by Ninja Kuma.
1 of my 3 polymorph tome spots.  This spot requires a high level mage character (the tome will only drop for mages), and can also be done with the potion of luck for a quick boost to profits.  Generally the kurzen monkeys in this spot have the highest chance to drop the Tome of Polymorh: Monkey – and the best part is they drop it often.  Always check your AH before deciding to farm this spot.  If theres not to many, then give it a try.  In the video I actually got more than one to drop.  It's the cheapest of the tomes, and consequentially the easiest to farm.  Again, you MUST be a mage.
From “The Burning Crusade” expansion, weapons like Klinge der Zauberei, Die Nachtklinge and recipes for different weapons are really valuable. The best example is Pläne: Teufelsstahlangschwert, worth 500.000+ Gold. These items are World Drops, you can find them in all raids and dungeons. I don’t know any Open World Drops, but that does not mean there are none. Another great transmog source are world bosses and rare spawns on Outland.