Personally I think using the chat features (Say,Shout,Yell,Tell,etc) should not break AFK status. That way all the RMT bots will be booted after 30 minutes. Or at least make it more of a hassle of the RMT vendors, having to program in AFK breaking patterns into their bots.

As for anyone that finds them self having a long chat session: move once in a while.