Sale #1:

https://backpack.tf/profiles/76561198353794340#!/compare/1546214400/1546560000

Bulk.

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Sale #2:

https://marketplace.tf/items/96;5;u18

Sold on December 8, 2018 for $33.

$33 / $1.68 = ~19.6

20 keys

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Sale #3:

https://marketplace.tf/items/96;5;u18

Sold on November 23, 2018 for $22

$22 / $1.74 = ~12.6

13 keys

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Sale #4:

https://backpack.tf/profiles/76561198317606171#!/compare/1546214400/1546300800

Bulk.

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Sale #5:

https://backpack.tf/profiles/76561198353392592#!/compare/1545868800/1546560000

Untracable.

Buyer at 12.6 keys shows 13 keys is too low.