Disco Fever

https://backpack.tf/item/2203661877

Sale 1) Sold for a Cloud 9 Hive Minder

https://backpack.tf/profiles/76561198053747026#!/compare/1505865600/1505952000

http://www.tf2outpost.com/trade/29371717 - Capped by the Buyout of 12 Keys

Sale 2) Sold for a Circling TF Logo Cadaver's Cranium (9 Keys) + 3 Keys

https://backpack.tf/profiles/76561198034098428#!/compare/1506211200/1506297600 - Buyer's Backpack

9 + 3 = 12 Keys

Cranium Mini

https://backpack.tf/profiles/76561198302402822#!/compare/1506124800/1506211200 - Sold for 9 Keys

https://backpack.tf/profiles/76561198296485477#!/compare/1506211200/1506297600 - Sold for a Spec KS Australium Force-a-Nature (~9.4 Keys)

Taking 9 Keys.

Sale 3) Sold for $27.99

https://marketplace.tf/items/330;5;u62

Keys were roughly $2 at the time. 27.99 / 2 = 13.995, which rounds to 14 Keys

Sale 4) Sold for $29.99

https://marketplace.tf/items/330;5;u62

https://marketplace.tf/items/5021;6/Mann%20Co.%20Supply%20Crate%20Key - Keys were $2 at the time

29.99 / 2 = 14.995, which rounds to 15 Keys