I'd personally love a smarter filtering system that looks at a combination of characters like $, plat, USD, www, @, etc, and simply disconnects the sender from the game entirely without sending the tell. Of course after a few weeks we'd be looking at completely unintelligible random spam, but there's other things to look at. Account age, trial, amount of people /told to, amount of tells that go unanswered, etc.
If they trip a few indications they could easily be booted.
Of course I'm sure filtering tells like that would add a lot of overhead