The answer is pretty simple, make it absurdly easy to get gold legally in 1370+ content. Before any haters jump in here and say there’s enough gold in the game already, I agree, but I’m not talking about not having enough gold. I’m talking about making gold so abundant through legal means, the risk of looking elsewhere for gold becomes less appealing. By taking away sources of gold income all that means is that gold sellers make more accounts to counter act the loss of previous income. This creates strain on the servers and long queue times for heavily affected areas. By increasing how much gold is available in the end game content, a place that a bit cannot enter and succeed, you decrease the feeling of the average player to look at RMT as a viable, about risky, way to get to where they want to go.
If you really want to Amber Heard in the gold seller’s beds, you could also decrease the necessity for gold in general. Such as a 5% decrease in the gold cost per honing attempt. By increasing the availability of gold and decreasing the necessity for having that much gold, you essentially limit any demand from the gold seller market.
Leave honing material drop rates the same. Or keep them at the pace you choose. Don’t inject more honing materials into the game to combat bots, I promise you it won’t work. What does work is taking a product, in this case illegally bought and sold gold, and make it essentially worthless. Just another arbitrary material.
Sure, the price of materials in the auction house will increase, that’s a given. But limiting the gold injection into content that bots can not realistically complete will offset that. Bots won’t be able to afford the materials to resell for profit.
Just as an aside, I have no problems making and keeping gold to do everything I want to do in this game. This is simply a proposed solution to an increasing problem.