Sale 1:

https://backpack.tf/profiles/76561198061376237#!/compare/1564790400/1564876800

https://backpack.tf/profiles/76561198047880917#!/compare/1564704000/1564876800

Sold for 15 keys (all other groups of items match with respective items)

Sale 2:

https://backpack.tf/profiles/76561198047880917#!/compare/1566086400/1566432000

https://backpack.tf/profiles/76561198156274478#!/compare/1566000000/1566086400

Sold with ~6 keys in sweets for KaW Ninja

use there

https://bot.tf/stats/listings/MGZ5NQ82

B/o of 18 keys

Sale 3:

https://backpack.tf/profiles/76561198156274478#!/compare/1567123200/1567209600

https://backpack.tf/profiles/76561198163755834#!/compare/1566604800/1567209600

Bulk

sale 4:

https://backpack.tf/profiles/76561198163755834#!/compare/1567814400/1568073600

https://backpack.tf/profiles/76561198387985735#!/compare/1567728000/1567814400

sold for ~12 keys

Sale 5:

https://backpack.tf/profiles/76561198387985735#!/compare/1567728000/1567814400

https://backpack.tf/profiles/76561198204215081#!/compare/1567728000/1567814400

Sold for Stormy Whoopee + 1 key

Whoopee mini:

https://backpack.tf/suggestion/5db154b7678072375026d6fe

Suggestion for 11 keys

Total is 12 keys

Sale 6:

https://backpack.tf/profiles/76561198204215081#!/compare/1571356800/1571443200

https://backpack.tf/profiles/76561198125894529#!/compare/1571356800/1571443200

https://backpack.tf/profiles/76561198204215081#!/compare/1571356800/1571443200

tradeback

sale 7:

https://backpack.tf/profiles/76561198162022281#!/compare/1568332800/1568419200

https://backpack.tf/profiles/76561198006097890#!/compare/1567987200/1568419200

Sold with 1 key for Smoking Wraith

Wraith mini:

https://backpack.tf/suggestion/5db1557dd381720da0692fd4

Suggestion for 17.5 keys

Total is 16.5 keys

https://bot.tf/stats/listings/Y9G7JO16

B/O of 17 keys

sale 8:

https://backpack.tf/profiles/76561198006097890#!/compare/1568419200/1568592000

https://backpack.tf/profiles/76561198131081286#!/compare/1568505600/1568592000

Sold for Smoking Noble(13.5) + ~2 keys in sweets

Total is ~15.5 keys

Sale 9:

https://backpack.tf/profiles/76561198131081286#!/compare/1569456000/1569542400

https://backpack.tf/profiles/76561198214895220#!/compare/1568937600/1569542400

Untrace

sale 10:

https://marketplace.tf/items/tf2/617;5;u33

$39.99 / $1.81 = 22.09 keys

https://backpack.tf/item/988677467

https://bot.tf/stats/listings/4JG66V8V

B/O of 18 keys, capping

Total sales @:

12, 12, 15, 15.5, 16.5, 18 keys

buyers up to 11 keys,

gonna exclude no sales,

taking the wide range of 12 - 18 keys