4 sales

1) SCM

https://backpack.tf/profiles/76561198355819006#!/compare/1547683200/1547942400

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2) ?

https://backpack.tf/profiles/76561198242229226#!/compare/1546732800/1546905600

https://backpack.tf/profiles/76561198305492646#!/compare/1546732800/1546819200

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3) Bulk

https://backpack.tf/profiles/76561198159855421#!/compare/1544572800/1545091200

https://backpack.tf/profiles/76561198305492646#!/compare/1544918400/1545091200

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4) https://marketplace.tf/items/319;5;u6

$29.99 on December 27th, keys were $1.79

29.99/1.79 ≈ 17 keys

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Total: 17

If you will find other sales, you're welcome to report them.