When we do trades we want to put the same message repeatedly. But the game prohibit doing that. So every each time we want to change the trade message and send it. It's pretty annoying. If people are spamming in real silence them. But the way game designed is even the deserved people can't publish the same message and making them annoyed.
Posting same message repeatedly is the definition of spamming. What do you mean? Also, spamming isn't silence able anymore, unless clearly done for causing disturbance/disruption.
As far as I know, you can post the same messages in public channels every 5 minutes. Its not really that long tbh