Classifieds at the time of posting this suggestion.

Unsolds are based on how long the listing has been up; Listing has been up 5 days and item been in the sellers inventory for 8 days? It has been unsold for 5 days.

The age of the listing(s) are shown in the screenshots rather than the last bump.

x3 for sale at ~2.1 Keys - http://i.imgur.com/762YQYW.png

Unsold for 6 days http://backpack.tf/item/4944710852

Unsold for 8 days http://backpack.tf/item/4107609670

Unsold for 11 days http://backpack.tf/item/4116362099

Outpost sellers.

http://www.tf2outpost.com/trade/28335995 - 2.1 Keys - Unsold for 1 week - Autobumper.