Proof: http://imgur.com/I89Pt7cHow it works:
The gil-sellers hack the terrain. They position themselves in walls, under the ground, and invisible (you can't see their character models, period). This prevents them from being interrupted or getting agro.
The next step is they bot/macro the nodes. I'm inclinded to believe it's a bot as opposed to a macro, given that they are on around a 20 second timetable per 4 nodes.
Furthermore, they teleport between nodes instantly. I'm not even sure how they manage that one, but they're legitimately insta-warping between nodes to maximize their time spent farming vs. walking.
This screen is from Central Thanalan, on the Ultros server. I'm sure you have these same types of people on your server, cheating the same way.
SE better get their **** together; this kind of stuff ruined FFXI, and if they don't seriously crack down on it, it's going to ruin FFXIV too.
Waiting for something fresh to arrive on the MMO scene...