Boat Party

https://backpack.tf/item/2355424278

Sale 1) ?

https://backpack.tf/profiles/76561198273094019#!/compare/1550102400/1550361600

https://backpack.tf/profiles/76561198363395191#!/compare/1550275200/1550361600

Sale 2) ?

https://backpack.tf/profiles/76561198363395191#!/compare/1556409600/1556496000

https://backpack.tf/profiles/76561198308841098#!/compare/1555286400/1556496000

https://backpack.tf/item/2551338562

Sale 3) Bulk sale

https://backpack.tf/profiles/76561198869144080#!/compare/1556323200/1556409600

https://backpack.tf/item/4554057174

Sale 4) Sold for 9 Keys + 19 Refined to a buy order

https://backpack.tf/profiles/76561198135785811#!/compare/1554681600/1555545600

https://imgur.com/a/PEwvfRQ

Low outlier.

https://backpack.tf/item/2001286462

Sale 5) ?

https://backpack.tf/profiles/76561198875470056#!/compare/1549324800/1549411200

https://backpack.tf/profiles/76561198132030750#!/compare/1549324800/1549497600 - The Keys here were involved.

Sale 6) ?

https://backpack.tf/profiles/76561198132030750#!/compare/1549497600/1549670400

https://backpack.tf/profiles/76561198002757046#!/compare/1549411200/1549497600

Sale 7) Sold for 11 Keys

https://backpack.tf/profiles/76561198002757046#!/compare/1550102400/1550188800

Sale 8) Quicksold for 11 Keys + 18 Refined

https://backpack.tf/profiles/76561198428134599#!/compare/1549929600/1550188800

Rounds to 11 Keys

Sale 9) Bulk sale

https://backpack.tf/profiles/76561198170045102#!/compare/1550102400/1550188800

Sale 10) Sold + 3 Keys + 11 Refined (0.25 Keys) for a Smoking Fed-Fightin' Fedora (14.5 Keys)

https://backpack.tf/profiles/76561198038307962#!/compare/1550188800/1550275200

14.5 - 3 - 0.25 = 11.25, which rounds to 11 Keys

Sale 11) Sold + 3 Keys for a Vicious Circle Highway Star

https://backpack.tf/profiles/76561198115074140#!/compare/1550188800/1550275200

https://backpack.tf/profiles/76561198370703651#!/compare/1550188800/1550275200

High outlier. Could probably be used to update the Star.

Sale 12) Looks like 10 Keys + Strange Scattergun

https://backpack.tf/profiles/76561198370703651#!/compare/1550448000/1550707200

https://backpack.tf/profiles/76561198175420885#!/compare/1550361600/1550448000

Sale 13) ?

https://backpack.tf/profiles/76561198175420885#!/compare/1550880000/1551052800

https://backpack.tf/profiles/76561198119634686#!/compare/1550966400/1551052800

Sale 14) Sold + ~0.3 Keys of Refined for a Bubbling Defiant Spartan (11.5 Keys) + 1 Key

https://backpack.tf/profiles/76561198886994914#!/compare/1552867200/1552953600

https://backpack.tf/profiles/76561198165205268#!/compare/1552867200/1552953600

11.5 + 1 - 0.3 = 12.2, which rounds to 12 Keys

Sale 15) Sold for an Orbiting Fire Buckaroos Hat (12 Keys)

https://backpack.tf/profiles/76561198165205268#!/compare/1553212800/1553299200

https://backpack.tf/profiles/76561198096006081#!/compare/1552780800/1553299200

Buckaroos Mini

https://backpack.tf/suggestion/5cbc202a6780721bee2f6eae - 12 Keys

Sale 16) Quicksold for 11 Keys

https://backpack.tf/profiles/76561198096006081#!/compare/1552780800/1553299200

https://marketplace.tf/items/181;5;u61 - Sold for $24.99 when Keys were ~$1.79 each

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

24.99 / 1.79 = 13.96, which rounds to 14 Keys

Calling this high due to the sheer number of sales at 12 or below.