It appears Japanese players are in agreement.

[Xieveral]

* Purchasing land or housing using gil obtained from RMT (real money trading) or other illicit means is strictily prohibited. Any land or estate hall deemed to have been purchased through such means is subject to seizure.

If it can be proven through investigation and most investigations don't happen until someone makes a report.

Unless the free company is named GoldCEO or asfdasdfasdf there's little cause for suspicion. But maybe they have a new detection method that doesn't rely on players to report illicit activity.