Apologies if this has been mentioned before, but I believe a good way to combat this would be to have some kind of in-game system in place where players (after proving they are trustworthy), have the ability to do something about the RMT accounts that are spamming us right then and there. For example, take a screenshot of the RMT spam so that you have proof that it was indeed a gilseller /tell, then either temp ban, or suspend the account. Who knows, my suggestion may not be practical, but I'm sure we could help in some way.
I do not frequent these forums as I spend all of my time in this game that I love, but after hearing of this thread I felt that I had an obligation to respond and add my name to this list. You have an amazing community SE, use us to your advantage, we can combat this together.
/signed Amprice Psyfon -Excalibur
