Sale 1:

https://backpack.tf/profiles/76561198804102808#!/compare/1589587200/1592092800

https://backpack.tf/profiles/76561198044934255#!/compare/1590537600/1590969600

https://backpack.tf/profiles/76561198041144544#!/compare/1592265600/1592438400

Untrace / MPTF?

sale 2:

https://backpack.tf/profiles/76561198041144544#!/compare/1592956800/1593216000

https://backpack.tf/profiles/76561198056681334#!/compare/1593129600/1593216000

Untrace / MPTF?

sale 3:

https://backpack.tf/profiles/76561198056681334#!/compare/1593216000/1593302400

https://backpack.tf/profiles/76561198055622215#!/compare/1593216000/1593302400

Bulk

sale 4:

https://backpack.tf/profiles/76561198055622215#!/compare/1593648000/1593734400

https://backpack.tf/profiles/76561198106784075#!/compare/1593475200/1593993600

Sold for 25 keys

sale 5:

https://marketplace.tf/items/tf2/208;15;u703;w4;pk252

$42.45 / $1.98 = 21.44 keys

$33.6 / $2.04 = 16.47 keys

https://backpack.tf/item/8560101447

sale 6:

https://marketplace.tf/items/tf2/208;5;u703;w4;pk252

$35 / $1.91 = 18.32 keys

Total sales @:

16, 18, 21, 25 keys

https://backpack.tf/classifieds?item=Alpine%20|%20Flame%20Thrower%20(Well-Worn)&quality=15&tradable=1&craftable=1&australium=-1&particle=703&killstreak_tier=0

Buyers on flamethrowers up to ~19 keys,

taking 21 - 25 keys.