Almost outdated. Using new sales only.

Sale 1:

https://marketplace.tf/items/tf2/539;5;u62

September 12: $61.66

$61.66 / $1.88 = 32.80 keys

Excluding from range because it's a day out of date, but I thought it may be useful to mention its existence.

Sale 2:

https://backpack.tf/item/1888714707

https://backpack.tf/profiles/76561198100879076#!/compare/1603497600/1603584000

https://backpack.tf/profiles/76561198432714467#!/compare/1603497600/1603584000

Used in bulk for a Tesla Coil Class Crown.

Sale 3:

https://backpack.tf/item/1888714707

https://backpack.tf/profiles/76561198432714467#!/compare/1603584000/1603670400

https://backpack.tf/profiles/76561199043177646#!/compare/1603584000/1603670400

Untraceable bot sale.

https://bot.tf/stats/listings/4EZWWDWK - B/O was 38 keys

https://bot.tf/stats/listings/MV6PQEDW - QB price was 33 keys, 3.11 ref.

Sale 4:

https://backpack.tf/item/1888714707

https://backpack.tf/profiles/76561199043177646#!/compare/1606003200/1606089600

https://backpack.tf/profiles/76561198119508247#!/compare/1606089600/1606262400

38 keys bot sale.

https://bot.tf/stats/listings/4WQVGK8X - bot B/O remained 38 keys

Sale 5:

https://backpack.tf/item/1888714707

https://backpack.tf/profiles/76561198119508247#!/compare/1606867200/1607299200

https://backpack.tf/profiles/76561198353865610#!/compare/1607126400/1607212800

34 keys, 8.88 ref (34.14), rounds to 34.

https://bot.tf/stats/listings/M1Z3DK01 - snapshot is close enough.

Sale 6:

https://backpack.tf/item/7956909841

https://backpack.tf/profiles/76561198140478853#!/compare/1600732800/1600992000

https://backpack.tf/profiles/76561198261919481#!/compare/1603670400/1607472000

Probable SCM sale by a scammer alt.

Sale 7:

https://backpack.tf/item/7956909841

https://backpack.tf/profiles/76561198261919481#!/compare/1606176000/1606262400

https://backpack.tf/profiles/76561199093588714#!/compare/1606176000/1606262400

Untraceable, but if the reviews on the "buyer's" page are to be believed, this was likely a successful scam.

Sale 8:

https://backpack.tf/item/7956909841

https://backpack.tf/profiles/76561199093588714#!/compare/1606262400/1606435200

https://backpack.tf/profiles/76561198905440732#!/compare/1606694400/1607558400

Untraceable, leading me to believe that this is just a furtherance of the scam.

Sale 9:

https://backpack.tf/item/7956821899

https://backpack.tf/profiles/76561198108872399#!/compare/1587513600/1600041600

https://backpack.tf/profiles/76561198057897812#!/compare/1600041600/1602547200

Untraceable. Seller's inventory is updated once in a blue moon. Can't even find out when it was traded by looking at the buyer's inventory.

Sale 10:

https://backpack.tf/item/7956821899

https://backpack.tf/profiles/76561198057897812#!/compare/1602633600/1602979200

https://backpack.tf/profiles/76561198098215462#!/compare/1602892800/1602979200

Untraceable. Looks like an SCM sale.

Sale 11:

https://backpack.tf/item/7955765301

https://backpack.tf/profiles/76561198395747553#!/compare/1604016000/1604188800

https://backpack.tf/profiles/76561197961465956#!/compare/1603756800/1604102400

Untraceable bulk for a Scorching Flames Brown Bomber.

Sale 12:

https://backpack.tf/item/7955765301

https://backpack.tf/profiles/76561197961465956#!/compare/1603756800/1604361600

https://backpack.tf/profiles/76561198080179568#!/compare/1604016000/1604102400

Bot QB for ~33 keys - https://bot.tf/stats/listings/4J5JQK39

Conclusion:

We have a few bot purchases and an entire history of scamming. None of the QBs can be included because of the current classified buyers: https://gyazo.com/3bdec5016e7e1b1fbd3a697aed8245ef

Taking the only useable sale, which corresponds with current sellers, at 38 keys.