Problems with automatic pattern recognition (Disclaimer - all domains are examples and not sites that I am aware of, any actual site that is included is purely coincidental):
How do you plan to pattern match that? Those are just a few possible examples off of an iPad keyboard. Once you're in a PC and have access to the full ASCII set... yeah, you're not going to pattern match anything. Relying on players to report strings being used so you can block them? There's so many possible variations that no one is going to spend time reporting more than one and your average player is just going to ignore it.
The only way to stop RMT is to make it not profitable and that's a very difficult thing to do without becoming the RMT yourself.