Hello,

Some ideas I can think of involve rate of /shouts and /tells a player can do. Legitimate /tell's will almost always have a back and forth with someone. If the amount of /tells they send doesn't come close to the amount of /tell's received from the person they /tell'ed, make the account.

/Shout's can be sometime similar. But the rate/amount of shouts can have an growing allow rate. i.e. shout once, have to wait 5 minutes. Shout again, have to 10 minutes. If the amount of shouts per account reaches a certain number per real day, shout is disabled for the rest of the day and the account is flagged.

It'd also be handy to have a server that pulls chat logs (snmp?) of /tells and/or /shouts nightly and parses it. With that, and a regex command, you can get a good amount of player names to mark for investigation for banning.

Of course, the best way to deal with this is to find the accounts that hold the gil that's being sold and ban them. That's just manual investigation work >.<