Online auctions and auction houses both come with fees.  Most auction houses add a ‘buyer’s premium’ above what the bidder bids.  Twenty (20%) to Twenty (25%) percent buyers premium is a common percentage added.  This will limit what a buyer can pay as it makes bidding too expensive yield a fair amount. Also, keep in mind, the point of buying at an auction is to get a good deal, not pay wholesale or retail. Therefore, bidders are looking to get diamonds for the least amount possible. Selling through auction houses rarely results in more money for the seller and requires you give up possession of your diamond before payment.