Resuggestion, thanks to K1ng for the info!

Sale 1:

https://backpack.tf/profiles/76561198106495563#!/compare/1562630400/1562716800

https://backpack.tf/profiles/76561198080179568#!/compare/1562630400/1562716800

QS

sale 2:

https://backpack.tf/profiles/76561198100484031#!/compare/1564876800/1565049600

https://backpack.tf/profiles/76561198012537041#!/compare/1564963200/1565049600

https://backpack.tf/profiles/76561198089253101#!/compare/1564876800/1564963200

https://backpack.tf/profiles/76561198287198615#!/compare/1565049600/1565136000

https://backpack.tf/profiles/76561198121830870#!/compare/1565049600/1565136000

Gambling

Sale 3:

https://backpack.tf/profiles/76561198121830870#!/compare/1565136000/1565222400

https://backpack.tf/profiles/76561198884518360#!/compare/1565222400/1565308800

Sold for Bubbling Defiant

use there

Sale 4:

https://backpack.tf/profiles/76561198884518360#!/compare/1565654400/1565740800

https://backpack.tf/profiles/76561198841279602#!/compare/1565568000/1565654400

Sold with ~1.5 keys in sweets for Planets Elfin

use there, most sales are above sellers

Sale 5:

https://backpack.tf/profiles/76561198165404585#!/compare/1562630400/1562716800

https://backpack.tf/profiles/76561198054273498#!/compare/1562544000/1562630400

Can only trace ~5 keys in sweets...

Sale 6:

https://backpack.tf/profiles/76561198054273498#!/compare/1564358400/1564531200

https://backpack.tf/profiles/76561198110825672#!/compare/1564358400/1564444800

Sold for Stormy Hetman

Hetman Mini:

https://backpack.tf/suggestion/5d9aaf26d3817222552eaf2c

Suggestion for 8.75 keys

Sale 7:

https://backpack.tf/profiles/76561198389557154#!/compare/1565049600/1565222400

https://backpack.tf/profiles/76561198121830870#!/compare/1564963200/1565049600

QS

Sale 8:

https://backpack.tf/profiles/76561198275862898#!/compare/1565308800/1565395200

https://backpack.tf/profiles/76561198287198615#!/compare/1565308800/1565395200

Bulk / Gambling

Sale 9:

https://backpack.tf/profiles/76561198287198615#!/compare/1565395200/1565481600

https://backpack.tf/profiles/76561198856721528#!/compare/1565395200/1565481600

https://backpack.tf/profiles/76561198323565601#!/compare/1565481600/1565568000

Gambling

Sale 10 - 12:

https://marketplace.tf/items/tf2/253;5;u35

$15.99 / $1.83 = 8.74 keys

$15.33 / $1.82 = 8.42 keys <-- https://backpack.tf/item/1123772728

$15 / $1.81 = 8.29 keys <-- https://backpack.tf/item/791116820

Total sales @:

8.29, 8.42, 8.74, 8.75 keys

K1ng's Part:

I see no real reason to exclude 8.75 with two sales at that. 8.29 rounds to 8.5, by the way, so this should be 8.5-9 instead.