Mini for another suggestion :P

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Sale #1 - No clue

https://backpack.tf/profiles/76561198012613726#!/compare/1561593600/1561680000

https://backpack.tf/profiles/76561198127514763#!/compare/1564444800/1565222400

Sale #2 - Spells

https://backpack.tf/profiles/76561198119629072#!/compare/1562284800/1562630400

https://backpack.tf/profiles/76561198185299778#!/compare/1562544000/1562630400

Sale #3 - 8 keys 3 ref

https://backpack.tf/profiles/76561198119629072#!/compare/1562803200/1562889600

https://backpack.tf/profiles/76561198273675032#!/compare/1562803200/1562889600

Sale #4 - https://marketplace.tf/items/tf2/935;5;u32 | https://backpack.tf/item/4250178663 | No clue on the b/o

16.67 / 1.81 = 9 keys

Sale #5 - Gamble

https://backpack.tf/profiles/76561198063075911#!/compare/1563321600/1563408000

https://backpack.tf/profiles/76561198038203241#!/compare/1563321600/1563408000

Sale #6 - Gamble

https://backpack.tf/profiles/76561198038203241#!/compare/1563408000/1563494400

https://backpack.tf/profiles/76561198072374854#!/compare/1562803200/1563494400

Sale #7 - Gamble

https://backpack.tf/profiles/76561198089253101#!/compare/1563408000/1563494400

https://backpack.tf/profiles/76561198072374854#!/compare/1562803200/1563494400

Sale #8 - Gamble

https://backpack.tf/profiles/76561198089253101#!/compare/1563580800/1563667200

https://backpack.tf/profiles/76561198044934255#!/compare/1563494400/1563753600

Sale #9 - No clue

https://backpack.tf/profiles/76561198833312246#!/compare/1565654400/1566777600

https://backpack.tf/profiles/76561198044934255#!/compare/1563494400/1563753600

Sale #10 - Bulk

https://backpack.tf/profiles/76561198833312246#!/compare/1565654400/1566777600

https://backpack.tf/profiles/76561198153088409#!/compare/1565568000/1565654400

Sale #11 - Sold with 3 keys in sweets for a TW pot (Better used there)

https://backpack.tf/profiles/76561198939932486#!/compare/1565740800/1565827200

https://backpack.tf/profiles/76561198153088409#!/compare/1565654400/1565740800

Sale #12 - Untrace

https://backpack.tf/profiles/76561198939932486#!/compare/1566000000/1566518400

https://backpack.tf/profiles/76561198002757046#!/compare/1565913600/1566000000

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Taking 8 - 9 keys

Unsold for 2 months at 9 supports

https://gyazo.com/ca89140d4e186e4b59b257ca98164935