Sale 1:

https://backpack.tf/profiles/76561198063075911#!/compare/1560988800/1561075200

https://backpack.tf/profiles/76561198012537041#!/compare/1560816000/1560988800

Untrace

Sale 2:

https://backpack.tf/profiles/76561198149688904#!/compare/1560816000/1561075200

https://backpack.tf/profiles/76561198337734785#!/compare/1560988800/1561075200

QS

Sale 3:

https://backpack.tf/profiles/76561198010707003#!/compare/1561593600/1561680000

https://backpack.tf/profiles/76561198855480250#!/compare/1561593600/1561680000

Sold for ~9 keys

sale 4:

https://backpack.tf/profiles/76561198132238434#!/compare/1565049600/1566000000

https://backpack.tf/profiles/76561198318342962#!/compare/1565740800/1566000000

Untrace

Sale 5:

https://backpack.tf/profiles/76561198203402208#!/compare/1566000000/1566604800

https://backpack.tf/profiles/76561198405547654#!/compare/1566000000/1567209600

Untrace

Sale 6:

https://backpack.tf/profiles/76561198049677507#!/compare/1563408000/1563494400

https://backpack.tf/profiles/76561198062797298#!/compare/1563494400/1563580800

https://backpack.tf/profiles/76561198062797298#!/compare/1563840000/1564531200

https://backpack.tf/profiles/76561198309563748#!/compare/1564444800/1564704000

Bulk

Sale 7:

https://backpack.tf/profiles/76561198322560312#!/compare/1565049600/1567641600

https://backpack.tf/profiles/76561198311322510#!/compare/1558915200/1565049600

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

Untrace

sale 8:

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

https://backpack.tf/profiles/76561198096621282#!/compare/1565136000/1565308800

Can trace 6 keys

Sale 9:

https://backpack.tf/profiles/76561198096621282#!/compare/1565136000/1565308800

https://backpack.tf/profiles/76561198087988539#!/compare/1564358400/1565136000

Sold with sweets for 7 keys

Total is ~6.5 keys

Sale 10:

https://backpack.tf/profiles/76561198840357141#!/compare/1561680000/1561766400

https://backpack.tf/profiles/76561198029074524#!/compare/1561680000/1561766400

Untrace

Sale 11:

https://backpack.tf/profiles/76561198886563850#!/compare/1561248000/1561334400

https://backpack.tf/profiles/76561198062290614#!/compare/1561161600/1561248000

https://backpack.tf/profiles/76561198073522694#!/compare/1561248000/1561334400

Untrace / gambling?

Sale 12:

https://backpack.tf/profiles/76561198169302585#!/compare/1561334400/1561420800

https://backpack.tf/profiles/76561198111543525#!/compare/1561334400/1561420800

Bulk

Sale 13, 14:

https://marketplace.tf/items/tf2/30836;5;u18

$17 / $1.82 = 9.34 keys

$16.32 / $1.78 = 9.17 keys <-- https://backpack.tf/item/5463875007

total sales @:

6, 6.5, 9, 9.17, 9.34 keys

buyers up to ~6.5 keys,

seller unsold for nearly a month at 9 keys,

gonna hesitantly say 6.5 - 9 keys, shouldn't exclude most sales...