This has been happening for years, people will take any Berserk art like fan colourings and such from the internet and try and make a profit from it. That Zodd one I've seen on eBay so many times, it's usually sold as a poster. I checked this guy out and he says it's officially licensed artwork. Yeah I doubt that. He just saved an image from the internet lol. But I doubt anyone can do anything about it sadly.
The real problem is that sites like Displate sustain themselves on the endless free art supply that users provide, under the auspices of it being art that they created. So even if someone flags it as unauthorized, it's in their best interest to ignore or delay the removal of any offending piece.