Looking at this item #1: https://backpack.tf/item/929289377

Sale #1

seller: https://backpack.tf/profiles/76561198025349704#!/compare/1589414400/1589673600

buyer: https://backpack.tf/profiles/76561198305494036#!/compare/1589500800/1589587200

listings at time of sale: https://bot.tf/stats/listings/4J923WG7

listings after sale: https://bot.tf/stats/listings/Y80J92DX

Sold for 15 keys.

Sale #2

seller: https://backpack.tf/profiles/76561198305494036#!/compare/1589673600/1589760000

buyer: https://backpack.tf/profiles/76561198219926077#!/compare/1589500800/1589760000

listings at time of sale: https://bot.tf/stats/listings/Y80JPJWZ

Sold for 16 keys 26 ref. Keys at the time makes that 16.5[sup]+[/sup] keys.

Sale #3

seller: https://backpack.tf/profiles/76561198219926077#!/compare/1590192000/1590278400

buyer: https://backpack.tf/profiles/76561198151928485#!/compare/1589932800/1592092800

listings at time of sale: https://bot.tf/stats/listings/YD151D2L

Seller for 16 keys 30 ref at the time was sold: see sale #5.

Sold for 18 keys.

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Looking at this item #2: https://backpack.tf/item/1457287089

Sale #4

seller: https://backpack.tf/profiles/76561198041103724#!/compare/1575763200/1593475200

buyer: https://backpack.tf/profiles/76561198313538268#!/compare/1593302400/1594080000

untrace? :S

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Looking at this item #3: https://backpack.tf/item/7889920473

Sale #5

seller: https://backpack.tf/profiles/76561198850178158#!/compare/1590192000/1590278400

buyer: https://backpack.tf/profiles/76561198041705595#!/compare/1590192000/1591056000

listings at time of sale: https://bot.tf/stats/listings/Y3WJ7ORQ

Same as sale #2, sold for 16.5[sup]+[/sup] keys.

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Additional evidence: bot sales

https://prnt.sc/tgkjh0

1 for 16.5[sup]-[/sup] keys

1 for 15.5[sup]+[/sup] keys

1 for 15 keys

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NO MP SALES: https://marketplace.tf/items/tf2/388;5;u19

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Current listings: https://bot.tf/stats/listings/4WXEQP80

buyers at 15.5 keys

unsold at 20 keys

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Going with 16-18 keys.