It's an old scam already, people will just write something random, add spaces and then fake a GM speaking. This method only works for the default size of a chat window, so if you want to avoid getting scammed, rezising your chat window gives you a clear view on who's trying to cheat on you.
They tend to do this:
And on your chat window, you get:
Note that if we enter anybody's chatroom, our names will be displayed on the list of players in the chatroom. So if you see us "speaking in your chatroom" but our names don't appear in the player list, it's obviously a fake.
Next time, screenshot when this happens to you and notify a GM via @request or file a ticket here. It's the same as making a new topic on the forums. Upload your screenshots and we'll solve the case.
We'll also look into your friend's login history to see if we can find this scammer.