Best way to avoid this kind of backlash is just to use the ingame reporting system via Menu>Support
This kind of behavior might best fall under "Exploits and Cheating".
Most of the time, the stuff that I run into falls under "Harassment and Conduct" or, at least, I'm assuming Code of Conduct stuff falls under this one.
Make sure that you include what server you are on. adding the global was a plus.
Also, I have seen the GM say to make sure to copy the name versus retyping it as some people switch characters that look like others like lowercase L and upper case i.
If you need to do a more detailed report, start it that way and then come to the forums. You'll find your reports under the "Support" tab at the top. You add more info there, including screenshots and links to videos.
And I agree, the behavior does seem strange. They maybe pricing their purchase below what the average bid is in the auction house and trying to pull a large quantity out of circulation for some market manipulation.
It is odd that someone would be doing this through chat (especially announcing that they want to purchase such a large market manipulating number), but that is the only way to circumvent the Market, and I don't think anyone uses the in-game trade or auction house channels.
Market PvP is much better when you aren't announcing the hand you're playing for everyone to see.