Teaching an old dog new tricks.

https://backpack.tf/item/246059428

Sale 1) Bulk sale

https://backpack.tf/profiles/76561198111127390#!/compare/1543017600/1543104000

Sale 2) Sold for 25 Keys

https://backpack.tf/profiles/76561198132844160#!/compare/1543363200/1543449600

Sale 3) ?

https://backpack.tf/profiles/76561198814957941#!/compare/1544227200/1544313600

Sale 4) Sold for 27 Keys

https://backpack.tf/profiles/76561198119634686#!/compare/1544486400/1544572800

https://backpack.tf/item/259630490

Sale 5) Sold for 23 Keys + ~0.25 Keys of Items

https://backpack.tf/profiles/76561198244963314#!/compare/1544745600/1545350400

https://backpack.tf/profiles/76561198268135738#!/compare/1544832000/1545350400

Low outlier.

Sale 6) Sold in 1 day for 24 Keys

https://backpack.tf/profiles/76561198268135738#!/compare/1545350400/1545436800

https://backpack.tf/item/206448932

Sale 7) Sold for 25 Keys

https://backpack.tf/profiles/76561198147955016#!/compare/1541116800/1541376000 - Buyer's Backpack

Sale 8) ?

https://backpack.tf/profiles/76561198147955016#!/compare/1541376000/1541980800

https://backpack.tf/profiles/76561198028759242#!/compare/1541721600/1541808000

Sale 9) ?

https://backpack.tf/profiles/76561198028759242#!/compare/1541808000/1541894400

https://backpack.tf/profiles/76561198105071091#!/compare/1541808000/1541894400

Sale 10) Sold + 5 Keys for a Cauldron Bubbles Safe'n'Sound (24 Keys) + Strange PDA (~13 Keys)

https://backpack.tf/profiles/76561198105071091#!/compare/1542412800/1542499200

https://backpack.tf/profiles/76561198071230830#!/compare/1542412800/1542499200

24 + 13 - 5 = 32 Keys

Sale 11) Bulk sale for a Sunbeams Industrial Festivizer

https://backpack.tf/profiles/76561198071230830#!/compare/1542499200/1542931200

https://marketplace.tf/items/322;5;u9 - Sold for $47.37 when Keys were ~$1.78 each

https://marketplace.tf/items/5021;6/Mann%20Co.%20Supply%20Crate%20Key

47.37 / 1.78 = 26.6, which rounds to 27 Keys