Markets always come and go in WoW. It can be a terrifying and painful experience when something you’ve been having great success with stops working. Hope is not lost though, there’s always something going on.
As long as there are players there is a market
As long as people play the game they will be willing to spend gold to reach their goals. If you’ve finished your raiding or PvP goals, you will spend much less on consumables and High-end BoEs. Some players will quit and wait for the next patch, others will look for alternative ways to enjoy the game. Cosmetic collections is a big one with toys, transmog, mounts and battle pets all offering a lot of work to get “finished”
Player totals and goals are the most important variables
The main thing that changes profitability and prices is when the game changes so players goals change, or the game is changed so the optimal way to reach a specific goal changes. Of course the amount of active players will also have an effect. When player counts dwindle as we head into the last part of a patch or expansion there will be slightly less economic activity, but it will never die completely.
Keep your finger on the pulse
Pay attention to public forums and discord to get an idea of what players are doing. Meme builds, transmog, specific new secret mounts and whatever else it can be. This will help you find new markets when something is trending downwards. Try to get ahead of the goldmaking pack rather than waiting for the guide to become public knowledge.
Good luck and happy market hunting.