It's very annoying when you're in Fort Blackstone and all you see in the chatbox is someone begging "can I have some gold" or "selling x for so much gold" only they repeat it over and over until it fills up the chatbox.
How about something that prevents them from posting the same message within so many seconds of the first one. Like if they paste "can I have some gold" within 10 seconds (or 30) of the first message, the system will tell them they can't. You can also make this where it is only effective in towns, because I've never seen this problem in a PvE group, and they could be booted anyway.
I know some annoying people will circumvent this by pasting and adding random characters to the end of their message, but who knows it might stop most of them. Another idea is to disable the ability to "paste" a message, but I don't know how many people use that for non-spamming reasons.
Also, I know I could add spammers to my ignore list but 1) I'd have to go find them and click their profile and 2) I'd rather save my ignore list for people who try to scam me or people who are jerks, so I know that they are all on there for a good reason and will be booted on sight. Otherwise I would have hundreds of people on it.