Item 1:

https://backpack.tf/item/8400325166

Sale 1:

https://marketplace.tf/items/tf2/30842;5;u3044

Sold for $22.5 on the 30th of July

Keys were $1.94 on the 30th

https://marketplace.tf/items/tf2/5021;6

22.5/1.94

= 11.59

Rounding up to 12 keys

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Item 2:

https://backpack.tf/item/6527272846

Mannco

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Item 3:

https://backpack.tf/item/6489026842

Sale 2:

https://backpack.tf/profiles/76561198151901778#!/compare/1748304000/1748736000

https://backpack.tf/profiles/76561199177132803#!/compare/1748304000/1748476800

Sold for 12 keys pure

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Item 4:

https://backpack.tf/item/6268470571

Sale 3:

https://backpack.tf/profiles/76561198056066720#!/compare/1741564800/1754956800

https://backpack.tf/profiles/76561199202090646#!/compare/1753315200/1753401600

https://next.backpack.tf/classifieds/snapshots/Static%20Shock%20Taunt:%20The%20Dueling%20Banjo/6882bbf391edd345fe12d6b5

https://imgur.com/a/EFCCVTh

8 keys match however bot had it listed at 14~ keys at the time it was sold, so 8 keys doesn't seem right so excluding

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Sellers:

BPTF - Technically one at 17 keys

MPTF - https://marketplace.tf/items/tf2/30842;5;u3044 - 1 @ 29.99

STN - https://stntrading.eu/item/tf2/Unusual+Static+Shock+Taunt%3A+The+Dueling+Banjo - None

SCM - https://steamcommunity.com/market/listings/440/Unusual%20Taunt%3A%20The%20Dueling%20Banjo?filter=Static+Shock - None

Sale(s):

12, 12

Going with 12 keys flat