Using the past 2 months.

Sale #1:

https://bot.tf/stats/item?def=1172&q=5&ef=Mega+Strike&craft=1&aus=0&ks=0

https://backpack.tf/profiles/76561198205065941#!/compare/1549584000/1549670400

Sold for 15 keys.

15 keys

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Sale #2:

https://backpack.tf/profiles/76561198373131137#!/compare/1552780800/1552867200

SCM Sale.

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Sale #3:

https://backpack.tf/profiles/76561198080179568#!/compare/1553299200/1553385600

Untraceable.

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Sale #4:

https://backpack.tf/profiles/76561198230732648#!/compare/1549584000/1549670400

Untraceable.

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Sale #5:

https://backpack.tf/profiles/76561198140501812#!/compare/1549670400/1551225600

Untraceable.

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Sale #6:

https://backpack.tf/profiles/76561197992659090#!/compare/1551571200/1551916800

SCM Sale.

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Sale #7:

https://backpack.tf/profiles/76561198053987078#!/compare/1552780800/1552867200

Sold with a Strange Professional Killstreak Hitman's Heatmaker (~3 keys) for a Spooky Night Taunt: The Schadenfreude (24 keys)

21 keys

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Sale #8:

https://backpack.tf/profiles/76561198883342894#!/compare/1553472000/1553558400

Bought for 10 keys and 20 ref.

10 keys

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Sale #9:

https://backpack.tf/profiles/76561198151568482#!/compare/1552262400/1552348800

Untraceable.

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Sale #10:

https://backpack.tf/profiles/76561198422289124#!/compare/1552348800/1552435200

Untraceable.

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Sale #11:

https://backpack.tf/profiles/76561198126976261#!/compare/1552348800/1552521600

Unsure.

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Sale #12:

https://backpack.tf/profiles/76561198158469471#!/compare/1549065600/1550275200

Unsure.

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Sale #13:

https://backpack.tf/profiles/76561198200785531#!/compare/1550966400/1551139200

SCM Sale.

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Sale #14:

https://backpack.tf/profiles/76561198200785531#!/compare/1551830400/1551916800

Unsure.

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Sale #15:

https://bot.tf/stats/item?def=1172&q=5&ef=Mega+Strike&craft=1&aus=0&ks=0

https://backpack.tf/profiles/76561198335791307#!/compare/1550530800/1550617200

Sold for 13 keys.

13 keys

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Sale #16:

https://marketplace.tf/items/1172;5;u3010

Sold for $15.

$15 / $1.80 = ~8 keys

8 keys

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Minis:

Spooky Night Taunt: The Schadenfreude:

https://backpack.tf/profiles/76561198053987078#!/compare/1552694400/1552780800

Sold for 23 keys and 45 ref.

24 keys

Sales:

8, 10, 13, 15, 21. Going with 10 - 15 keys.