Eventually, I came up with another thing, I'll add it to the main topic as post edit, buy would be this:
Instead of doing a quest at a certain point. Detect if someone does too many tells every 5 minutes, if that happens, activate the verify protocol for fooling the boots, doing some captcha or code, or something that would require human intervention... I think this is even better than the whole idea I just made before because it is not expected... Unlike what happened with the idea before... I realized that the persons behind the bots would just go and activate the tell commands and so, then they forget until the bot is banned, it reduces a little the thing... But this way they'd have to be actively checking bots... And that's really a bothering for them, this one would reduce it even more and it wouldn't suppose such a nuisance for the players.
It is like if you put 7 fishing bots. Maybe some of you noticed it or not, but when you are fishing in the same area too much time, a strange message that I don't remember appears, and it is clearly made for avoiding a bot fishing 5 hours or more nonstop, so someone have to go there and move the bot. With the tells it could be the same.
Every certain tells per minute, send a prompt. The time that it takes to reply this prompt will be the time needed for use tell again... so if a bot takes 5 hour because the person behind noticed it failed, 5 hours will have to wait again for sending a tell... If a player replies in less of a minute to this prompt-captcha-whatever you want to call it... Player will be able to continue replying and a new prompt won't appear until next 24h...
Of course, as I said, this won't exterminate RMT as long as they are winning money with this, but highly, efficiently reduce their activity because the need of having to do manual things all the time.
PS: I put the fishing example because was a good idea by SE, but the 'prompt' they use is not a proper one and could easily be bypassed, idea would be to do something similar to that with the tells, but really requiring of an intelligent response or of rationalize.