This needs a drop.

Sale #1:

Sold with two painted Purple Cosmetics, Détective Noir and Rogue's Col Roule for a Smoking Master's Yellow Belt:

http://www.tf2outpost.com/trade/27082284

Seller's backpack before: http://backpack.tf/profiles/76561198177736182?time=1443015333

Seller's backpack after: http://backpack.tf/profiles/76561198177736182?time=1443078000

Total: ~19 keys

Mini Suggestion for the Belt:

Sold for 19 keys:

Seller's backpack before: http://backpack.tf/profiles/76561198131562491?time=1440895045

Seller's backpack after: http://backpack.tf/profiles/76561198131562491?time=1440918000

Out of the 20 keys, only one key's history doesn't match so it sold for 19 keys rather than 20 keys.

Sale #2:

Sold for a Kill-a-Watt Infernal Impaler and 5 keys:

http://www.tf2outpost.com/trade/26934971

Total: (13*0.9) + 5 = 16.7

Rounding it up to 17 keys

Mini Suggestion for the Impaler:

Offered with 2 keys for an Orbiting Planets Tyrant's Helm:

http://www.tf2outpost.com/trade/26617739

Total: 15 - 2 = 13

Mini Suggestion for the Tyrant's:

http://backpack.tf/vote/id/560bac00dea9e9712a19625b (Credits to Jacobmeister)

Please tell if I have made a mistake.