Honestly, RMT spam is the worst I've ever seen it in a modern MMO in FF XIV. I would think that there would be some effort made to prevent this like only allowing paid accounts with level 15+ characters to be able to send /tells unless the recipient is on their friends list or something. This would make the spam accounts at least have to put forth a little effort before spamming and being banned.

Also, it seems like they could easily update the UI so that you could instantly report RMT spammers by right-clicking on a spammers name and reporting them for RMT spam. These spammers would then get a message stating that they are not allowed to send /tells until a GM reviews the report and bans them (or not). This should only trigger after they receive 5 or more reports within a short period (like two hours), so that players cannot use it to send false reports.