Sale 1:

https://backpack.tf/profiles/76561198398370775#!/compare/1529712000/1530057600

https://backpack.tf/profiles/76561198046477272#!/compare/1529625600/1529798400

Sold for items?

Sale 2:

https://backpack.tf/profiles/76561198046477272#!/compare/1531008000/1531180800

https://backpack.tf/profiles/76561198114402400#!/compare/1531008000/1531180800

Bulk.

Sale 3:

https://backpack.tf/profiles/76561198114402400#!/compare/1534464000/1534550400

https://backpack.tf/profiles/76561198320715865#!/compare/1533945600/1534550400

Untrace.

Sale 4:

https://backpack.tf/profiles/76561198320715865#!/compare/1534636800/1534723200

https://backpack.tf/profiles/76561198077396836#!/compare/1534636800/1534723200

Untrace.

Sale 5:

https://backpack.tf/profiles/76561198077396836#!/compare/1534723200/1534809600

QS

Sale 6:

https://backpack.tf/profiles/76561198349886701#!/compare/1532908800/1532995200

https://backpack.tf/profiles/76561198042663181#!/compare/1532908800/1533168000

Sold for 20 keys? Contradicts Sale 7

Sale 7:

https://backpack.tf/profiles/76561198042663181#!/compare/1533254400/1533340800

https://backpack.tf/profiles/76561198274549672#!/compare/1533254400/1533340800

Sold for 19 keys? Contradicts Sale 6

Sale 8:

https://backpack.tf/profiles/76561198232956880#!/compare/1530403200/1530489600

https://backpack.tf/profiles/76561198302774496#!/compare/1530316800/1530489600

Sold for Insomnia Big Topper

Topper Mini:

https://backpack.tf/suggestion/5b7e61cc44325a6b1c7d9571

Suggestion for 17 keys

Sale 9:

https://backpack.tf/profiles/76561198302774496#!/compare/1530576000/1530662400

https://backpack.tf/profiles/76561198002757046#!/compare/1530576000/1530662400

Sold for 18 keys + 21 ref

Sale 10:

https://backpack.tf/profiles/76561198002757046#!/compare/1530921600/1531008000

https://backpack.tf/profiles/76561198316655937#!/compare/1530835200/1531267200

Untrace, probably 21 keys. Based off of Sale 12

Sale 11:

https://backpack.tf/profiles/76561198316655937#!/compare/1531267200/1531353600

QS

Sale 12:

https://backpack.tf/profiles/76561198002757046#!/compare/1531440000/1531526400

https://backpack.tf/profiles/76561198155587390#!/compare/1531440000/1531526400

Sold for ~21 keys in items

Sale 13:

https://backpack.tf/profiles/76561198155587390#!/compare/1531526400/1531612800

https://backpack.tf/profiles/76561198074518443#!/compare/1531440000/1531526400

Sold for CH Sky High + 4 keys

Sale 14:

https://backpack.tf/profiles/76561198074518443#!/compare/1531612800/1531699200

https://backpack.tf/profiles/76561198313364985#!/compare/1531440000/1531699200

Sold for 17 keys

Sale 15:

https://backpack.tf/profiles/76561198313364985#!/compare/1531699200/1531785600

https://backpack.tf/profiles/76561198082684654#!/compare/1531612800/1531699200

Sold for 18 keys + ~1 key in Fabricators(yes, Fabs.)

Total is 19 keys

Sale 16:

https://backpack.tf/profiles/76561198082684654#!/compare/1531958400/1532131200

https://backpack.tf/profiles/76561198396499936#!/compare/1532044800/1532131200

Bulk

Sale 17:

https://backpack.tf/profiles/76561198396499936#!/compare/1532304000/1532390400

https://backpack.tf/profiles/76561198096247397#!/compare/1532304000/1532390400

Bulk

Sale 18:

https://backpack.tf/profiles/76561198096247397#!/compare/1532390400/1532476800

https://backpack.tf/profiles/76561198125791160#!/compare/1532390400/1532476800

Bulk.

Sale 19:

https://backpack.tf/profiles/76561198125791160#!/compare/1533945600/1534032000

https://backpack.tf/profiles/76561198143117018#!/compare/1533945600/1534032000

Sold for TW Drill Hat + 1 key

Drill Hat Mini:

https://backpack.tf/suggestion/5b7e64facf6c757a8975ef8e

Suggestion for 19.5 keys

Total is 20.5 keys

Sale 20:

https://marketplace.tf/items/523;5;u29

Sold for 44 USD

Keys at 1.98 USD

Total is 22.22 keys

Total sales @:

17, 17, 18.64, 19, 20.5, 21, 22.22

Let's go with 17 - 22 keys.