What you will need:
Trial Account
Non Trial Account
First what you will need to open up two wow clients. Log on to the non trial wow and make a new toon, example "Erich"
Run to your Major City and make this macro. /camp
On the Trial account make a character called Erich and get ready to click create.
Ctrl C this message. /dnd WTS CHEAP WOW GOLD "YOUR SITE ETC" PRICE ETC
Now on your non Trial account type "/2 Quitting wow, pst me if you want my gold" Press enter the immediately /camp macro, delete the character and Alt tab on to the other wow
On the Trial account you prepared earlier press create character, who has the same name and log in and spam on the loading screen. ctrl V
You can speak to people on trial accounts if you are replying to them.
In a Nutshell
They see the message in trade, they start typing to you. By the time they reply to you, you are already on the trial account with the same name ready for it to automatically reply to them
/dnd WTS CHEAP WOW GOLD "YOUR SITE ETC" PRICE ETC
So the Aim of this is to safely advertise gold without getting your main account banned