If your wanting to increase your gold here are a few things you can do.

Your main maker is obviously the auction house.

Use your profession wisely. You can make lower and higher level items, and throw them on the auction house.

Also, RAW materials sell so good. Are you a miner? Sell the new and old ore. People will buy what you sell.

Something I did alot, I would go around to all of the old vendors in towns and some sell a random item or two. It could be a pattern, item, or weapon. It wouldn’t be a bad idea to throw them on the auction house as well.

If your questing never vendor the greens always sell.

I hope this helps a little bit its all I could think of .
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