There are other ways to combat this though. We know gil sellers will continue making accounts. We know people will continue buying gil. What do people complain about though? It's the /tell spam we all get every single hour we're logged in. It's the most horrid in this game as I've ever seen in an MMO. That is something that can be easily fixed by some simple solutions:
  1. First, limit the chat capabilities of accounts with no characters over level 5. Take away their ability to /tell anyone unless they are mutual friends and unless someone /tells them first. This should have minimal impact on any real people playing and starting the game, and it will inconvenience the RMT's and make them have to spend more time getting a spam bot set up. And time is money, so that will hurt their pockets.
  2. Second, limit the amount of tells someone is able to send out in a small amount of time. If someone sends more than 15 tells within 3 seconds, lock them to a timer so they can't send anymore for a minute or two.
  3. Couple the above with a report spam feature as mentioned by Sacred-Oblivion. If their /tells hit a certain percentage that gets reported (say 70% after a total of 15 messages), then ban the account from chatting completely until an investigation concludes.

Congrats, SE, without a whole lot of effort, reduces RMT spam to near nothing, because it will NOT be profitable for the RMT's to spend $15 on a new account just to be able to advertise to a handful of people, and they'll eventually stop completely.

The RMT spam will migrate to other means and you'll probably only ever see lowbies standing in major cities spamming /s, which the report spam should also shut down relatively quickly. But your ignore list will be useful for toxic players and not just an RMT name bank.