Credits to Lemonade and FishCrimes for the first 2 sales.

https://backpack.tf/item/3350097818

Sale 1) Sold for 25 Keys

https://backpack.tf/profiles/76561198085347196#!/compare/1544227200/1544313600

IDs don't match because the hat was painted, but the IDs are really close.

Sale 2) Sold + ~3 Keys of Items for a Blizzardy Storm Dark Falkirk Helm (32 Keys)

https://backpack.tf/profiles/76561198218238955#!/compare/1544313600/1544400000

https://backpack.tf/profiles/76561198057541872#!/compare/1544313600/1544486400

32 - 3 = 29 Keys

Falkirk Mini

https://backpack.tf/suggestion/5c1b2780cf6c757c12661ed8 - 32 Keys

Sale 3) Sold + ~3 Keys of Items + 2 Keys for a Bubbling Crone's Dome (39 Keys)

https://backpack.tf/profiles/76561198057541872#!/compare/1544918400/1545004800

https://backpack.tf/profiles/76561198102188526#!/compare/1543276800/1545004800

39 - 3 - 2 = 34 Keys

Crone's Mini

https://backpack.tf/suggestion/5c195855cf6c757b372c5d7c - 39 Keys