Sale #1:

Sold for 31 keys:

https://backpack.tf/profiles/76561198058996177#!/compare/1514937600/1515283200

https://backpack.tf/profiles/76561197963500354#!/compare/1514851200/1514937600

Sale #2:

Sold for 28 keys:

https://backpack.tf/profiles/76561198111640529#!/compare/1514678400/1514764800

Too close to the buyers' price, not using

Sale #3:

Sold for a Green Energy Backbiter's Billycock:

https://backpack.tf/profiles/76561198103009390#!/compare/1513296000/1514592000

https://backpack.tf/profiles/76561198045692488#!/compare/1514073600/1514160000

Total: 35 keys

Sale #4:

Sold mine to a buyer for 27 keys and 10 refined:

https://imgur.com/a/sgKlc

Sale #5:

Sold for 35 keys:

https://backpack.tf/profiles/76561197963500354#!/compare/1510444800/1510531200

Sale #6:

Sold with 2.5 keys worth of sweets for a Professional Killstreak Australium Sniper Rifle + Uncraftable Fancy Fedora:

https://backpack.tf/profiles/76561198313782481#!/compare/1510963200/1511049600

https://backpack.tf/profiles/76561198218886139#!/compare/1510876800/1511136000

Valuing the Sniper Rifle at 39 keys:

https://backpack.tf/classifieds?item=Sniper%20Rifle&quality=11&tradable=1&craftable=1&australium=1&killstreak_tier=3

Rounds up to 37 keys

Sale #7:

Sold with ~2 keys worth of sweets for a Circling Heart Defiant Spartan:

https://backpack.tf/profiles/76561198158482500#!/compare/1511913600/1512000000

https://backpack.tf/profiles/76561198057034390#!/compare/1511913600/1512000000

Total: 35 keys

Mini suggestion for the Spartan:

Sold for a Circling Heart Scotch Bonnet and Director's Vision Unusualifier:

https://backpack.tf/profiles/76561198050036339#!/compare/1515542400/1515628800

Total: 37 keys

Mini Suggestion for the Bonnet:

Sold for a Max's Severed Head and 2 keys:

https://backpack.tf/profiles/76561198050036339#!/compare/1512086400/1512691200

Total: ~22 keys

Sale #8:

Bulk for a Green Energy Dr's Dapper Topper:

https://backpack.tf/profiles/76561198057034390#!/compare/1511913600/1512000000

Bulk, not using

Sale #9:

Sold in a day for 26 keys:

https://backpack.tf/profiles/76561198106495563#!/compare/1511913600/1512000000

https://backpack.tf/profiles/76561198357846994#!/compare/1511827200/1512000000

Quicksell, not using

Sale #10:

Sold in a day for 28 keys

https://backpack.tf/profiles/76561198357846994#!/compare/1512950400/1513209600

https://backpack.tf/profiles/76561198103009390#!/compare/1512777600/1513209600

Quicksell, not using

Sale #11:

Sold for 29 keys and ~2 keys in sweets:

https://backpack.tf/profiles/76561198293654690#!/compare/1511222400/1511308800

https://backpack.tf/profiles/76561197963500354#!/compare/1511222400/1511308800

Total: 31 keys

Sale #12:

Sold for 26 keys:

https://backpack.tf/profiles/76561198267189538#!/compare/1511222400/1511308800

Low, not using

Credits to JoXu for sales 5, 6, 7, 8, 9, 10, 11 and 12