Add the ability to right-click on a player character's name in chat, Report Player.

That /report function may include RMT, Racial Slurs, Sexual Slurs, etc.

When reported, copy the lines written by that reported player so that Square Enix may review the text. Remember, some people would abuse /report and innocent people can be accused, so it is important to have non-biased review of /reported players.

Here is where /report can put an end to Gil Sellers:

If a player attains 25 /reports within a 10 minute period, LOCK their account until it is reviewed by Square Enix. 25 /reports by separate people, not the same individuals. This would ensure that the person being /reported is engaged in an activity that is disrupting gameplay for many people and should be stopped.

Many Gil Sellers are using compromised accounts, so locking them can help to solve many problems.