100% agree that something needs to be done. It's just blatant RMT being ignored by SE. Even certain world first groups allegedly participate heavily in these activities. We all know what these guys mean when they ask to talk only on discord.
Either officially allow this form of RMT or make advertising of sell runs that only allow communication through discord or other 3rd party programs/websites bannable and force discussion of gil payment to be in-game.

Currently this form of RMT seems to be implicitly allowed by SE.