Try something a little different.

Sale 1:

https://backpack.tf/profiles/76561198819564432#!/compare/1564099200/1564185600

https://backpack.tf/profiles/76561198126590077#!/compare/1564185600/1564272000

Bulk

Sale 2:

https://backpack.tf/profiles/76561198065792603#!/compare/1564790400/1565049600

https://backpack.tf/profiles/76561198393588133#!/compare/1564963200/1565049600

Sold for 29 keys

Sale 3:

https://backpack.tf/profiles/76561198393588133#!/compare/1565827200/1566000000

https://backpack.tf/profiles/76561198093251141#!/compare/1565740800/1566000000

Sold for 35 keys

Sale 4:

https://backpack.tf/profiles/76561198093251141#!/compare/1566000000/1566086400

https://backpack.tf/profiles/76561198077555267#!/compare/1566000000/1566086400

Sold for HG Coldsnap

use there

https://bot.tf/stats/listings/M17ZQ9GO

B/o of 40 keys

Sale 5:

https://backpack.tf/profiles/76561198077555267#!/compare/1566086400/1566172800

https://backpack.tf/profiles/76561198079182224#!/compare/1566086400/1566172800

Sold for 29 keys

Sale 6:

https://backpack.tf/profiles/76561198079182224#!/compare/1567728000/1567900800

https://backpack.tf/profiles/76561198002757046#!/compare/1567814400/1567900800

Sold for 28 keys(?)

Sale 7:

https://backpack.tf/profiles/76561198002757046#!/compare/1567900800/1567987200

https://backpack.tf/profiles/76561198261265788#!/compare/1567900800/1567987200

Sold for 32 keys

Total sales @:

28, 29, 29, 32, 35 keys

Note that during the time of the 29 sales, buyers were only ever up to 27 keys:

https://bot.tf/stats/listings/4OV6Z2VQ

https://bot.tf/stats/listings/Y7D91LQ9 <--- 29 seller even had a buyout of 30 keys.

https://bot.tf/stats/listings/Y5RZ7D73

knowing this,

calling 28 low (buy order),

not excluding 35,

Taking 29 - 35 keys