If a character/account has been blacklisted by 25 or more accounts in a single zone over a certain finite period of time, say an hour or so, that character should be automagically flagged for immediate review and temporarily blocked from using shout, tells, etc.

That character should receive an in-game mail advising them of their restrictions and that they should wait for contact by a CSR who will review the situation. If the account appears to be a normal account, the CSR should determine if the player was inordinately out of line and offensive, is a gil seller account or was hacked and is being taken advantage of.

Use of shout, /tells to strangers, etc. is a privilege, not a right.

I'm not a database wiz but am pretty sure there would be a way to determine this on a regular basis with batch processes, if not in real time.