Exactly this. There is only 1 sale in all of 2014 (excluding his) for a book in similar grade...which is guess what the 3.5. He posted a link to it and said here is a similar book have at it. He didn't strong arm anyone to purchase the book at his price, nor did he "manipulate sales". This is no different than saying hey I saw a NM 98 cgc 9.8 sell for 1k the other day on ebay here is the link. Mine is only 950 shipped.
I think you are missing the general concern. It's not actually the price at all. It's the fact that the book was a highlight in a well advertised auction from a notable auctioneer. Only hours later does it appear for sale here on the boards and who knows where else. Is it against the board rules to ask questions before sending someone 19k? For all we know the scans could have simply been ripped and it's obvious to some of us that can clearly see what exactly is going down. The seller is playing it without letting on that the book remains CC and quite frankly these details just need to be brought to light IMO. Again the price is not a big a deal as the play for the sale.
"Playing on air" comes to mind in the world of playing pool. You "play on air" and lose, depending on what kind of bar you are at, it could mean an asskicking. Regardless of the hobby or business endeavor - selling, wagering or representing something you don't have is not an acceptable practice that people are usually 'ok' with.
Except on Wall St. (where margin buying is a mainstay)