There are several online auction platforms for coins, some are even numismatic specific. My question is what is missing from current platforms?
Members. This is why eBay has a monopoly. The day I see an Auction/BIN/OrBestOffer type site that rivals eBay, I am all in. Currently, there is not a one that comes close; both in quantity or quality.
if its an auction site, let it be an auction site IMO than a site that offer(s) bin/ best offer ( whats the point of it, besides being lazy surfing the net to find it )