Hi there,
we all know, that trading in the global chat can be pretty annoying sometimes, if it comes, that your posts are spammed away by some trashtalk, guild recruitement posts or other stuff. But auction isn't an alternative if you wanna sell your stuff fast. People keep spamming their "WTS" posts like any 30-60 seconds in order to display them in the chat.
So I suggest, implementing an additional default global chat channel, every player has access to, only for trading (for example by command /trade). This chat channel could be displayed in the general chat tab, too, but should have the option to (un-)activate it in the chat settings as well. So players could add another tab only for trading to filter the useless stuff out of the chat.
In other MMO's this already is a standard, which is very useful for players, because we all are traders somehow, some more, some less. And if you need a megaphone for usage, Idc.
Best regards
Zyrex