One thing that has become abundantly clear lately is that players flock to the same methods. Through youtube, reddit, even my blog players congregate to the same proven methods, and jump on the current flavor of the month.
When everyone does it, profits drop
The more people are doing something the less profitable it is. With higher quantities on the AH it’s going to take significantly more time for items to sell out at the current price. This will eventually force players to post at lower prices to entice more buyers.
This usually happens in every goldmaking method in the game. More players farming the same item will drive the price down.
Good methods are popular
Of course every good goldmaking method will be popular, and most of them are well known. Everyone knows you can often craft consumables profitably. Everyone knows farming current expansion herbs work. They will still look for the single most effective way to do it, or the newest method and use that.
Popularity is an indication that it works, and you should not be afraid of a market that has players in it.
Higher profit margins can be found elsewhere
If you want to increase your profit margins however, looking for new markets can be well worth it. There will always be methods that are unpopular or out of favor, just because they are not getting publicity. Tons of old world crafted markets are consistently producing gold, including enchanting tomes, panthers and other items that always retain value.
Even with the current market situation in BfA where the seller side is completely flooded with players going for their Brutosaurs there will be less crowded markets.
Use the tools available
Use sites like theunderminejournal.com to look for items with higher prices and less competition. There are so many items in the game at this point that you can always find one with low enough competition that you can profit from it.
A method you work out yourself will likely be way less crowded than one you learned about from me, or youtube, so utilize that fact.