Let's start with this: if you have /say or /shout enabled, you're asking for headaches like this. Turn everything but FC, LS, group, and whispers off. There is no reason to have anything else enabled. I'm not defending S-E on this either, as I do think they need to do a better job of this. But you can absolutely never see /say or /shouts from gold sellers, and it doesn't take away anything meaningful from your day-to-day.

What would be nice, however, is if S-E could code in a filter for players. I'm talking something along the lines of the WoW add-on Bad Boy. I'm only providing the link for those who don't know what it is. When I was playing WoW, this one add-on got rid of all the spam and unwanted whispers for me. If it can be maintained by an add-on author, certainly S-E is more than capable of adding something similar in-game.