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 - Unsolds and item histories are presented in chronological order according to the screenshot(s).

x1 for sale at 6 Keys - http://i.imgur.com/sosppFo.png

Unsold for 9 days - http://backpack.tf/item/1078881269

Outpost sellers.

http://www.tf2outpost.com/trade/28405566 - 6.15 Keys - Unsold for 2 weeks.