They went underground because it was too easy to spot and report them when they just floated up out of reach in the air on their cookie cutter template THMs.

They've been doing this since before there was a free trial of the game. Adding the free trial just means they can mitigate some of their risk by not paying for a full version until it's accumulated things to sell. Though apparently free players cannot hold more than 300K gil and have no retainer or marketboard access and I think no ability to trade either.

Its possible they're aware of the bots and just flagging them for action to be taken when they transition out of free version to paid version so they can see who it interacts with at that point in an attempt to trace and remove more of the actual RMT accounts conducting the actual business.