It shouldn't be too hard, I just don't think they have a dedicated team or enough GMs to cover the grounds..

It should be as simple as triggering red flags for people who sent /tells to more than 20 people within the span of an hour.
Then taking a look at the content of the messages..

Figure about a dozen RMT spammers on a server each.. That could be reviewed with 2 people max once they implement a system that flags the potential offenders, I think the capacity to log and filter chats are just lacking on SE's side.

I've even seen frauds posted in the forums where SE wouldn't do anything about it because their investigation didn't show up with anything even when the person had posted all the chat logs from the incident.. (i.e. Highly likely they don't keep chat logs) think about how stingy they are with the servers regarding everything else that take up extra data, I wouldn't be surprised.