One place worth of note is the raid Tomb of Sargeras, and especially on mythic difficulty. The reason for this is that some of the tier pieces are only available through BoEs (the warrior belt namely being one of them), so if you happened to get your hands on one of those, you could earn a good sum of gold out of it. Other places would also be the newest raids from the expansion Battle of Azeroth, as they are also often tied to similar set pieces.
While they likely won’t sell right away, you will likely sell them at some point, and they usually sell for a good chunk of gold, so it is indeed a good gold maker (to an extent)
Old raid Boes, such as tomb of sargeras, antorus, theese boes sell for about 10k-150k depends on the server and difficulty you get it from. Also in bfa you can farm world drop mounts+you will get a lot of abbysal crystals with it too.Theese mounts are realy high even as far as 400k. And abbysal crystal when you get 20 it is basicaly mount so it is worth some 100-200k too even more all depends on server economy.