I've played a few other MMOs. One of the features in many of them is that directly above the chat box window is usually a few check boxes that let you turn on and off different chats. Local, trade, and guild just as examples. Everybody is complaining about spamming and the hard to read chat, this might fix it. Another thing that may help keep people keep trades to the respective chat is if any chat posts starting with "WTS" or "WTB" automatically get put into the trade chat (unless specifically said in guild chat). I've seen this done before also and it greatly helps keep trades out of local chat.

~Gwen