https://marketplace.tf/items/tf2/517;5;u9 - The duped one sold for $200 (104 Keys)

https://backpack.tf/profiles/76561198274544005#!/compare/1635379200/1635552000 - 65 Keys + Pro KS Big Kill (~11 Keys at the time)

https://backpack.tf/profiles/76561198274544005#!/compare/1636070400/1636156800 - Sulphurous Detective Noir (89 Keys)

Noir sales:

https://backpack.tf/profiles/76561198311297599#!/compare/1632960000/1633046400 - Bulk

https://backpack.tf/profiles/76561198331167728#!/compare/1635638400/1635811200 - 73 Keys

https://backpack.tf/profiles/76561198199244659#!/compare/1635638400/1635811200 - Added 20 Keys for a Frozen Icefall Brain Bowl (125 Keys)

Taking 73 to 105 for the Noir averages to 89 Keys

With Buyers at 77.6 Keys, I'd go 76 to 89 here using the Big Kill and Noir sales. It wouldn't be ideal to eliminate 75% of the usable sales because of buy orders that have been rapidly rising and weren't this high when any of these sales happened.