Make gold untradable and account bound. Force all transactions through the auction house. The local economy becomes a trade economy, as in ill trade a pearl for that bag, and the global economy becomes a market that analytics could be used to find abusers. If you wanted to cash out you would have to sell goods to a vendor that buys for much less than the market and would essentially be a tax. It would solve inflation and gold selling at the same time.
The problem isn’t unsolvable, it just comes at a cost that Blizzard has no intention of paying. They make too much money off of it. The WoW token wasn’t to stop anything, it was to redirect profits from bot subscriptions to actual sales. They didn’t want to lose the money, they just wanted to change the means of obtaining it.