What I would do against goldsellers, if I would be Funcom:
I would enable a script which logs all transaction about money transfer on the server.
Next I would create a BAIT-character and level to Tortage
Then I would buy 100 Gold from a gold seller for my bait-toon
Now I would check my toon from which character I got 100 gold and so I get an ACCOUNT name, because I am Funcom and I can look at the accounts
I would check money on all toons of this account and watch all transactions FROM and TO this account for the next 2-3 days and the days already passed since starting my logging. I´m confident that I will find a network of other characters (and so: other accounts) who transfer money from one to another. Some of them will have thousands of gold.
Last but not least I would ... NOT ban them - but reduce all coins to ZERO on all characters of all accounts which had a connection in the logs because they were buying gold or a dealers of the "big fishes".
Let´s see who will complain.