Sale 1:

https://backpack.tf/profiles/76561198114086974#!/compare/1545004800/1545091200

https://backpack.tf/profiles/76561198289040457#!/compare/1545004800/1545091200

Bulk

Sale 2:

https://backpack.tf/profiles/76561198289040457#!/compare/1545091200/1545264000

https://backpack.tf/profiles/76561198119415784#!/compare/1543968000/1545264000

Sold for 35 keys

Sale 3:

https://backpack.tf/profiles/76561198192602363#!/compare/1547337600/1547424000

https://backpack.tf/profiles/76561198049312442#!/compare/1547337600/1547424000

Bulk

Sale 4:

https://backpack.tf/profiles/76561198000326258#!/compare/1543104000/1543276800

https://backpack.tf/profiles/76561198381983721#!/compare/1543190400/1543276800

Sold for Isotope Terror FT Scattergun

Use there

Sale 5:

https://backpack.tf/profiles/76561198381983721#!/compare/1543363200/1543449600

https://backpack.tf/profiles/76561198254882979#!/compare/1543363200/1543449600

Sold for 32 keys

Sale 6:

https://backpack.tf/profiles/76561198254882979#!/compare/1544832000/1544918400

https://backpack.tf/profiles/76561198799666244#!/compare/1544832000/1544918400

Sold for Insomnia Virus(32) + ~9 keys in sweets

Total is 41 keys

Sale 7:

https://backpack.tf/profiles/76561198799666244#!/compare/1547942400/1548028800

https://backpack.tf/profiles/76561198098563620#!/compare/1547942400/1548028800

Sold for Blizzardy Samur-Eye(26) + Blizzardy Bombing + 1 key

Bombing Mini:

https://backpack.tf/suggestion/5c61f02444325a71314316e3

Suggestion for 9.5 keys

Total is 36.5 keys

Sale 8:

https://backpack.tf/profiles/76561198098563620#!/compare/1548633600/1548720000

https://backpack.tf/profiles/76561198309237889#!/compare/1548201600/1548633600

Sold for 23 keys + G Fetti Brian Warming

Any Mini for Brain would end up at ~9 keys, taking that

Total is 32 keys

Sale 9:

https://backpack.tf/profiles/76561198309237889#!/compare/1548633600/1548720000

https://backpack.tf/profiles/76561198068156546#!/compare/1548633600/1548720000

Sold for 32 keys

Sale 10:

https://backpack.tf/profiles/76561198068156546#!/compare/1548720000/1548806400

https://backpack.tf/profiles/76561198247600746#!/compare/1548633600/1548720000

Sold for 31 keys? Countered by Sale 9

Sale 11:

https://backpack.tf/profiles/76561198247600746#!/compare/1549584000/1549843200

https://backpack.tf/profiles/76561198003698220#!/compare/1549670400/1549756800

Sold for 32 keys

Sale 12:

https://marketplace.tf/items/183;5;u8

Sold for 66 USD

Keys at 1.70 USD

Total is 38.82 keys

Total sales @:

31, 32, 32, 32, 35, 36.5, 38.82, 41 keys

Sellers at 40 keys,

Buyers up to 31 keys,

Considering 32 sales all sold quickly, and one being a bit iffy (Sale 11-12),

taking 35 - 39 keys.