Completed trades are examples of an agreement between buyer and seller. Searching sellers of shades on OP shows many completed trades at their price of 2 refined. Still, concrete proof for you:

http://tf2tp.com/trade.php?trade=8813052 (2ref)

http://tf2tp.com/trade.php?trade=8849916 (2ref)

http://tf2tp.com/trade.php?trade=8816474 (2ref)

Unfortunately searches on OP for buyers pretty much all turn up all shitty craft hat buyers that get ignored (obviously), and we can't see completed trades for people who only wanted a pair of shades, whether this would complement my proof or detract from it.