"Nintendo is pleased with the co-operation it has received from both eBay and Amazon to prevent the sales of game copying devices," Nintendo's global head of anti-piracy, Jodie Daughtery told MCV. eBay has actually pulled auctions for copying devices for years (presumably as an "item encouraging illegal activity), so if there is a policy update, it involves even more vigilant policing of auctions.
Amazon UK games director Chris Poad told MCV that Amazon has a "notice and take down" process for its third-party Marketplace. "So where a third party believes that their IP has been infringed, they can highlight it and we can take it down. This is what happened in the case of the R4."
Now Nintendo just has the rest of the Internet to deal with in its efforts to curtail DS piracy (and, as an extremely unfortunate side effect, homebrew).