https://marketplace.tf/items/tf2/617;5;u58

Sep 20 - $59.99 / $1.85 = 32.43 keys

Sep 24 - $39.99 / $1.84 = 21.73 keys

Dec 1 - $59.99 / $1.76 = 34.09 keys

Dec 10 - $59.99 / $1.82 = 32.96 keys (key price taken from average of the week, rather than the day)

https://backpack.tf/item/7957324432

https://backpack.tf/item/7957532267

https://backpack.tf/item/9031003336

https://backpack.tf/profiles/76561198142127847#!/compare/1599177600/1600992000

https://backpack.tf/profiles/76561198337734785#!/compare/1600905600/1600992000

Only refined matches

https://backpack.tf/profiles/76561198141187659#!/compare/1602806400/1602892800

https://backpack.tf/profiles/76561198839638687#!/compare/1602374400/1602806400

Untraceable

https://backpack.tf/profiles/76561198082858261#!/compare/1605225600/1605398400

https://backpack.tf/profiles/76561198061464918#!/compare/1605225600/1605312000

21 keys

https://backpack.tf/profiles/76561198061464918#!/compare/1605657600/1605744000

https://backpack.tf/profiles/76561198280643788#!/compare/1605657600/1605744000

28 keys

https://backpack.tf/profiles/76561198280643788#!/compare/1607040000/1607212800

https://backpack.tf/profiles/76561198090457223#!/compare/1607126400/1607212800

Delightful Star Taunt: Didgeridrongo

Better used on the taunt

https://backpack.tf/profiles/76561198090457223#!/compare/1607212800/1607299200

https://backpack.tf/profiles/76561198362263986#!/compare/1607212800/1607299200

23 keys

https://backpack.tf/profiles/76561198362263986#!/compare/1607126400/1607212800

https://backpack.tf/profiles/76561198131633162#!/compare/1607126400/1607212800

24 keys

A situation

Sales:

21

22

23

24

28

32

33

34

Buyers to 24 keys

https://gyazo.com/eda02a008109edca1d6dd62e2f4f272a

Despite being half of the sales, all of the 24 key sales were indeed same/1 day sales or that one MP dump.

Going with 28-34