Our trader won't ask you to return your gold after trading for any reason(screenshots, bonus, banned account and so on). Anyone who does that is a scammer! If you return your gold, we won't take your loss!
How did it happen?
Since when the scammer saw you and our trader were together, your toon level is high and our trader's level is 1 usually, he just guessed your guys were trading. Then he created a toon name like our trader's and used a reason to threaten or scam you.
It's easy to create a new toon in wow in seconds.