As I'm mostly playing Lord of the Rings Online nowadays, I only log on my WoW characters occasionally to do things like alchemy transmutes, jewelcrafting, or auction house buying and selling. This means I usually log on my level 70 warrior alchemist and my level 70 priest jewelcrafter only as long as it takes to do their craft, then send all the stuff to a level 42 shaman who is my auction house mule. The level 42 is on longer than the level 70s. Nevertheless the level 42 never gets any tells or spam WoW mails advertising gold. Only the level 70s do. Apparently the gold sellers assume that mostly the level 70s are buying gold.
Now when Blizzard bans gold farmer accounts, they ban over 100,000 of them at one time. I'd say that nearly all of these are playing on US and European servers, players on Chinese servers are probably less rich and less interesting as customers. Divided by about 400 total servers that makes 250 gold farmers per server. Each of them making in excess of 1,000 gold per day this produces a *lot* of gold. Who is buying all this? Some of it is certainly bought by casual players not wanting to grind money for their various mounts. But I would figure that casual players don't need that much gold in total, 2,000 covers the essential first three horses, and casual players buy very little of the high-end consumable stuff, like potions and enchants. Playing solo usually produces more gold than it consumes.
Raiding on the other hand is a money sink, it consumes far more gold than it produces. A single Gruul raid can cost over 1,000 gold in potions and stuff. And it is the raiders who need all those expensive primals and other materials for enchantments to keep on the very top of things. Now there are certainly raiders who have the time to grind for all that gold or materials themselves. But not everyone does. The fact that gold farmers target level 70 players with their advertising suggests that it is them who buy most of it. Raiding itself and preparing for it with attunements and grinding reputations is time-consuming enough, I wouldn't be surprised if many raiders "outsourced" their gold farming to a gold seller. Of course they'd never admit it, the hardcore players are a lot more concerned about their image than the casual players. But I just don't see casuals consuming all that much virtual gold, while the cost of raiding is well-known and often discussed.
Makes me wonder how much of the upcoming changes to Alchemy, reducing the number of potions used in a raid significantly, are Blizzard's way of fighting gold farmers.