SE tried a word filter for blocking tells in FFXI to stop RMT tells back around 2009... and it worked... for about a week. Then the RMT companies figured out what words were being blocked, and simply adjusted the messages they were sending out (usually by using creative wording in the tells, such as website addresses using substitution ciphers to avoid blocking web addresses. Then the RMT returned with a vengeance.

As much as I hate RMT and are annoyed by their constant spam (or was - I haven't gotten an RMT tell on Balmung since Heavensward launched) , a word filter does not work because no matter what SE does the companies will always be trying to overcome SE's attempts at blocking them. It's a zero sum game that SE simply cannot win I'm afraid.

Really, SE needs to make the penalties for those who actually buy this ill-gotten gil far harsher than what they are (such as, blacklisting the player's real life identity from ever playing the game again) as a deterrent to try and kill their actual business. Because RMT would have no reason to exist if no one actually bought their gil in the first place.