Thank you Scourge for this suggestion and two month's premium!

Sale 1:

https://backpack.tf/profiles/76561198755285882#!/compare/1566000000/1568592000

https://backpack.tf/profiles/76561198141111993#!/compare/1561075200/1569801600

Untrace

sale 2:

https://backpack.tf/profiles/76561198087931314#!/compare/1567555200/1569888000

https://backpack.tf/profiles/76561198363395191#!/compare/1567555200/1567728000

Sold for 9 keys QS

Sale 3:

https://backpack.tf/profiles/76561198363395191#!/compare/1568592000/1568678400

https://backpack.tf/profiles/76561198285967572#!/compare/1568678400/1568851200

https://backpack.tf/profiles/76561198363395191#!/compare/1568937600/1569024000

Untrace

Sale 4:

https://backpack.tf/profiles/76561198164911027#!/compare/1566432000/1566518400

https://backpack.tf/profiles/76561198090750997#!/compare/1566432000/1566518400

Sold with 8 keys for TW Woodsman

Woodsman Mini:

https://backpack.tf/suggestion/5db14346d381720446267009

Suggestion for 19.5 keys

Total is 11.5 keys --> 12 keys

Sale 5:

https://backpack.tf/profiles/76561198090750997#!/compare/1566518400/1566604800

https://backpack.tf/profiles/76561198304302520#!/compare/1566518400/1566604800

Sold for 10 keys (QS)

Sale 6:

https://backpack.tf/profiles/76561198192602363#!/compare/1566172800/1566259200

https://backpack.tf/profiles/76561198419935413#!/compare/1566172800/1566259200

Untrace

sale 7:

https://backpack.tf/profiles/76561198261347875#!/compare/1569456000/1569628800

https://backpack.tf/profiles/76561198894761128#!/compare/1569542400/1569628800

Scammer QS

Sale 8:

https://backpack.tf/profiles/76561198337734785#!/compare/1570233600/1570320000

https://backpack.tf/profiles/76561198321179399#!/compare/1570233600/1570320000

Keys

Sale 9:

https://marketplace.tf/items/tf2/183;5;u57

$34.99 / $1.82 = 19.23 keys --> 19 keys

Total sales 2:

9, 10, 12, 19 keys

9-10 too low, quicksells as stated above.

12-19

12 supported