The only MMO I know of that has absolutely 0 gold sellers is Planetside 2. Why? There is no in game player-tradable currency. The problem of combating gold-farming bots is not a simple one, for a variety of reasons.
Without going into to much detail on the root causes of the problem - those that create botting programs are typically skilled programmers / scriptwriters that treat creating botting / hack tools as a full time job. Automatic detection systems can only take you so far - after all, securing a system intended to be private is difficult enough. Securing one intended to allow thousands of players to connect and interact is another problem entirely.
In my opinion, Zenimax should really hire a few full time people to chase bot reports. Making bot reporting easier would go a long way as well.
I can't tell you how many times i've given up trying to report bots due to laggy, nonresponsive multipage forms (In several cases, these have actually triggered a crash).
• Add an option to the context, right click menus for player names, "Report Bot / Spammer" , after which that player is automatically added to your ignore list, complete with a text message that you have done so (To mitigate accidentally selecting this.)
• Even 2 full time guides / GMs on each mega-server would go a long way, offering a free sub to qualified players in exchange for an hour or so of bot-chasing would be awesome. With access to a real-time list of players in a given region, spotting potential bots, even without player reports. If you see someone named oashfpoqw, and find that they are flying beneath the ground yoinking every resource in sight... Yeah, it's probably a bot.
• Add an automated bounty system for reports. In the event a Zenimax employee / system / sanctioned player GM determines that a report is correct, and the bot is banned... award the first 5 or so reporters with a bounty box, which can contain small amounts of gold, a random item near their level, etc. This system even has the potential to make the bots turn on each other, as the larger organizations attempt to eat the smaller ones, or drive them out of business.
Thoughts?