Not an accusation as much as a suspicion due to the lack of transparency on the seller's part regarding the adoption process. I do see in the ad description, "They have been taken to events and "discovered,", but have not been otherwise circulated or handled."
Obviously I have overlooked the collectors niche as possibility however, I would think the proper avenue for notification would be to eBay rather than Groundspeak. This raises other questions such as are coins placed in geocaches 'contributed' to the sport where it is now up to Groundspeak to defend ownership of stolen goods? While the original purchasers of the coins can prove ownership, it seems a stretch to expect to maintain control of the coin while you pass it around the world. In this case, collectors who harm the sport by permanently removing them from caches so they can keep them are actually worse then those that attempt to sell them since the sellers haven't actually removed ownership from the original purchaser, they have just made it more difficult for the coin to get to the next geocache...