SE can use their logs to map the flow of goods and gil from player to player.

When they find out who they all are, they can come down in one fell swoop and take out a few thousand with perma bans. As they go through it all, they need to ID the payment accounts as well to insure they ban the source of payment.

All in all, it cant stop all of it forever, but they can make it much much more costly for anyone running a business selling gold to NEWB's.