Sale #1:

https://backpack.tf/profiles/76561198218379705#!/compare/1545868800/1545955200

Sold with 4 keys for a Terror-Watt Kiss King (21 keys)

17 keys

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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 keys

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 keys

13 keys

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Minis:

Terror-Watt Kiss King:

https://backpack.tf/profiles/76561198218379705#!/compare/1546473600/1546560000

Sold for 21 keys

21 keys