Most of the "worthless coins being sold on
ebay for big bucks" are for cashless money laundering purposes.
It goes something like this. Criminal A gives Criminal B something illegal (proceeds of crime, illicit substances, unlicensed weapons, etc). To facilitate paying for it, Criminal A also lists on
ebay a worthless coin for the price specified, telling Criminal B the item's description to look for. Criminal B "buys" the coin, paying for it on Paypal or whatever. Criminals A and B both now have "money from sale of rare coin" on their books, as far as law enforcement and the tax man are concerned. Whether Criminal B ever actually gets the coin in question is irrelevant, as Criminal B never actually wanted the coin in the first place.
It's allowable on
ebay because coins under $2500 are not required to comply with
ebay's strict coin-selling requirements (must be slabbed, etc). If more than $2500 needs to be transferred, then multiple "coin sales" must take place, or some other method of money transfer is chosen.
Of course, if some innocent bystander were to happen see the coin listed for sale and bid on the coin, all the better; Criminal B would get their ill-gotten goods for free, and Criminal A doesn't care, so long as somebody pays them. But the whole thing is supposed to fly under everybody's radar, unnoticed. The only people who would notice "there's something fishy here" are coin collectors who know that a worn, damaged, unremarkable coin with fuzzy pictures and no description explaining its rarity shouldn't be worth that much. And we're supposed to just ignore it as a crackpot asking moon money for a worthless coin, rather than go and blab about it on an open Internet forum.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis