Sale #1:

https://marketplace.tf/items/31008;5;u111

Sold for $25.

$25 / $1.75 = ~14 keys

14 keys

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Sale #2:

https://marketplace.tf/items/31008;5;u111

Sold for $33.90.

$33.90 / $1.79 = ~19 keys

19 keys

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Sale #3:

https://backpack.tf/profiles/76561198360722961#!/compare/1552694400/1552780800

Untraceable.

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Sale #4:

https://backpack.tf/profiles/76561198007696852#!/compare/1550880000/1550966400

Untraceable.

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Sale #5:

https://backpack.tf/profiles/76561198876584040#t7582911292

Sold with 1 key for a Green Confetti Conjurer's Cowl (15 keys)

14 keys

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Minis:

Green Confetti Conjurer's Cowl:

https://backpack.tf/profiles/76561198094382760#!/compare/1551052800/1551139200

Sold with ~2 keys for a Circling Peace Sign Antarctic Eyewear (16.5 keys)

15 keys

Sales:

14, 14, 19. Going with 14 keys.