Feel free to report the $17,000 item, it's in violation of
ebay's "no raw coins to be listed over US$2500" policy.
I've always assumed most of these offerings - especially the ones you actually see in the "sold items" sort - are drug deals, or some such criminal money-laundering attempts. It's the perfect cover: you buy $800 worth of drugs (or stolen goods or whatnot), and pay for it by "buying" this coin on
ebay: once the payment goes through, they send you the goods. And now, both people have on their books "$800 paid for sale of rare coin", all above board and legal if any cops or tax agents come snooping. The only people who know that that coin isn't really worth $800 are actual coin collectors, who are smart enough to simply ignore the listing.
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