The most efficient message filter addon of Vanilla.
Command: /ignoreplayer
This addon filters all the messages by performing keyword match check.
You can type /ignoreplayer in game to add any key words involved in gold selling or anything else you dont wanna see.
I've collected some key words when i played on this vanilla server.
If you check "Name" option it will only match key words with player's name instead of their messages.
Let's see how it works，here is an emotion message of gold selling advertisement sent by the gold farmers ,but Ignoreplayer filtered it ,it didnt show up in my chat window.
here is another emotion message from the infamous gold farmers,but it got filtered as well.
choose different key words of a message in case it doesn't work. they would change the content of advertisements sometimes,so make sure to update the key words yourself once these ads appear again.