Karate Kards

https://backpack.tf/item/2620590868

Sale 1) Sold for a Purple Confetti Shooter's Sola Topi (13 Keys) + 11 Keys

https://backpack.tf/profiles/76561198027694776#!/compare/1496620800/1496880000

31 + 11 = 24 Keys

Sale 2) Sold for a Miami Nights Scotsman's Stove Pipe + 1 Key

https://backpack.tf/profiles/76561198195483499#!/compare/1497139200/1497225600

http://www.tf2outpost.com/trade/29219429 - Buyout was 24 Keys, so this sale is capped at that or fits in the range.

Sale 3) Sold for a Steaming Dr's Dapper Topper (22 Keys)

https://backpack.tf/profiles/76561198267189538#!/compare/1497830400/1497916800

Sale 4) Sold + 4 Keys + ~1 Key of Items for a Smoking Dr's Dapper Topper (23.5 Keys)

https://backpack.tf/profiles/76561198234339160#!/compare/1499990400/1500076800 - Buyer's Backpack

23.5 - 4 - 1 = 18.5, which rounds up to 19 Keys

Dapper Mini

https://backpack.tf/suggestion/5995d915cf6c753d9268dc49 - 23.5 Keys

Sale 5) Sold for a Blizzardy Storm Scotsman's Stove Pipe (13 Keys) + Haunted Ghosts Magnificent Mongolian (12 Keys)

https://backpack.tf/profiles/76561198138645673#!/compare/1500336000/1500422400 - Buyer's Backpack

13 + 12 = 25 Keys

Stove Mini

https://backpack.tf/suggestion/599763b7cf6c75731f5dc057 - 13 Keys

Sale 6) Sold for an Electric Hat Protector Universal Translator + 1 Key

https://backpack.tf/profiles/76561198138645673#!/compare/1500508800/1500595200

Fits in the range.

https://backpack.tf/item/4888005272

Sale 7) Sold for a Circling TF Logo Jumper's Jeepcap (22 Keys)

https://backpack.tf/profiles/76561198153301791#!/compare/1498867200/1499385600

http://www.tf2outpost.com/trade/29236833 - Capped by the Buyout of 20 Keys

Sale 8) Sold + 1 Key for a Bubbling Safe'n'Sound + Blizzardy Storm Bolted Birdcage

https://backpack.tf/profiles/76561198095022965#!/compare/1499644800/1499731200 - Seller's Backpack

https://backpack.tf/profiles/76561198173442901#!/compare/1499644800/1499731200 - Buyer's Backpack

http://www.tf2outpost.com/trade/29269406 - Capped by the Buyout of 22 Keys