Sale 1-3:

https://marketplace.tf/items/tf2/151;5;u30

$18 / $1.78 = 10.11 keys // https://backpack.tf/item/2108627893

$18 / $1.77 = 10.17 keys

$24.99 / $1.75 = 14.28 keys

Sale 4:

12 keys

https://backpack.tf/profiles/76561198986177898#!/compare/1583366400/1583452800

https://backpack.tf/profiles/76561198354459626#!/compare/1583366400/1583452800

Sale 5:

9 keys

https://backpack.tf/profiles/76561198063556736#!/compare/1581638400/1581724800

https://backpack.tf/profiles/76561198308772967#!/compare/1581552000/1581724800

Sale 6:

bulk for keys

https://backpack.tf/profiles/76561198308772967#!/compare/1583280000/1583366400

https://backpack.tf/profiles/76561198026129220#!/compare/1583280000/1583366400

Sale 7:

11 keys

https://backpack.tf/profiles/76561198108448982#!/compare/1584316800/1584403200

https://backpack.tf/profiles/76561198963954159#!/compare/1584316800/1584403200

Sale 8:

untrace

https://backpack.tf/profiles/76561198963954159#!/compare/1585180800/1585267200

https://backpack.tf/profiles/76561198108448982#!/compare/1585180800/1585267200

Sale 9:

9 keys + 7 ref

https://backpack.tf/profiles/76561198108448982#!/compare/1585180800/1585267200

https://backpack.tf/profiles/76561198827124516#!/compare/1585180800/1585267200

Sale 10:

7 keys? maybe something missing?

https://backpack.tf/profiles/76561198827124516#!/compare/1585353600/1585440000

https://backpack.tf/profiles/76561198071082937#!/compare/1585353600/1585440000

Sale 11:

10 keys

https://backpack.tf/profiles/76561198071082937#!/compare/1585440000/1585526400

https://backpack.tf/profiles/76561198171624643#!/compare/1585440000/1585699200

Sale 12:

10 keys

https://backpack.tf/profiles/76561198021055079#!/compare/1584403200/1584489600

https://backpack.tf/profiles/76561198079989511#!/compare/1584403200/1584489600

Sale 13:

using on pillar

https://backpack.tf/profiles/76561198079989511#!/compare/1586044800/1586217600

https://backpack.tf/profiles/76561198080425549#!/compare/1585958400/1586044800

Sale 14:

9 keys + 31 ref

https://backpack.tf/profiles/76561198080425549#!/compare/1586044800/1586131200

https://backpack.tf/profiles/76561198066237738#!/compare/1586044800/1586131200

Sale 15:

10 keys

https://backpack.tf/profiles/76561198066237738#!/compare/1586044800/1586131200

https://backpack.tf/profiles/76561198271371098#!/compare/1585008000/1586131200

Sale 16:

untrace

https://backpack.tf/profiles/76561198271371098#!/compare/1585008000/1586131200

https://backpack.tf/profiles/76561198146259385#!/compare/1586044800/1586131200

Sale 17:

untrace

https://backpack.tf/profiles/76561198146259385#!/compare/1586131200/1586217600

https://backpack.tf/profiles/76561198394963563#!/compare/1585958400/1586131200

Sale 18:

untrace

https://backpack.tf/profiles/76561198394963563#!/compare/1585958400/1586131200

https://backpack.tf/profiles/76561198095027292#!/compare/1583712000/1586131200

==============================================================================

Sales:

9,9,9.5,10,10,10,10,10,11,12,14

14 high outlier

buyers at 9.2 keys: https://imgur.com/a/0gQYVH4