No you don't. Look at this suggestion: http://backpack.tf/vote/id/566eebf5dea9e9b2067f7667

If a sale happens at a certain price, and someone else has got a listing for quite some time at a lower price, it means this lower price is not a quicksell, and that means you can price the hat with that, since the sale at a superior price suggests so. The hat has got to be clean, and the seller active enough, of course. I don't know how this applies in this particular case, but sometimes sales is not the only thing used to price an unusual.