Burning Flames Backbiter's Billycock

https://marketplace.tf/items/tf2/108;5;u13

https://backpack.tf/item/2682874216

https://backpack.tf/item/277441332 - sold for $135 (71 keys), $120 (64 keys)

https://backpack.tf/profiles/76561198125917042#!/compare/1592006400/1592697600

https://imgur.com/a/0bN2wzC - sold for 53 keys

https://backpack.tf/profiles/76561198850178158#!/compare/1593734400/1593907200

https://backpack.tf/profiles/76561198139171368#!/compare/1593734400/1593820800

https://bot.tf/stats/listings/4EP5OZ0Q - sold for 55 keys + 40 ref (56)

https://backpack.tf/profiles/76561198043826027#!/compare/1591920000/1592870400

https://backpack.tf/profiles/76561198119458888#!/compare/1592697600/1592870400 - bulk for something

https://backpack.tf/profiles/76561198304302520#!/compare/1590364800/1590451200

https://backpack.tf/profiles/76561198142552263#!/compare/1590537600/1591142400 - may 31 marketplace sale

https://backpack.tf/profiles/76561198342161127#!/compare/1594339200/1594425600

https://backpack.tf/profiles/76561198014468512 - sold with 7 keys for Scorching Flames Grenadier's Softcap (59) = 52 keys

https://backpack.tf/profiles/76561198139171368#!/compare/1594166400/1594252800

https://backpack.tf/profiles/76561198128141636#!/compare/1594252800/1594339200 - sold with Cool Festivized Professional Killstreak Flower Power Medi Gun (Factory New) for Time Warp Sergeant's Drill Hat (better to use there)

https://backpack.tf/profiles/76561198119634686#!/compare/1593648000/1593820800

https://backpack.tf/profiles/76561198139171368#!/compare/1593734400/1593820800 - sold for 55 keys

https://backpack.tf/profiles/76561198848059175#!/compare/1591920000/1592006400

https://backpack.tf/profiles/76561198119634686#!/compare/1591920000/1592006400 - sold for 52 keys

https://steamuserimages-a.akamaihd.net/ugc/1463058338079941770/CAD5A2241B40D2F6238D1C41FB6A87C078F5C3FF/

https://backpack.tf/profiles/76561198210678091#!/compare/1591920000/1592006400 - sold for Green Energy Condor Cap (48.5) + 8 keys = 57 keys

https://backpack.tf/profiles/76561198069493147#!/compare/1591660800/1591833600

https://backpack.tf/profiles/76561198210678091#!/compare/1591660800/1591833600 - sold with Circling Heart Swagman's Swatter for some amount of keys

https://backpack.tf/profiles/76561198301649793#!/compare/1591574400/1591660800

https://backpack.tf/profiles/76561198069493147#!/compare/1591488000/1591660800 - sold with spelled Strange Professional Killstreak Scotsman's Skullcutter for Flaming Lantern Towering Pillar of Hats (could be used there)

https://backpack.tf/profiles/76561198305494036#!/compare/1587340800/1587427200

https://backpack.tf/profiles/76561198218628708#!/compare/1587340800/1587427200

https://imgur.com/a/0bN2wzC - sold for 55 keys

Conclusion:

sales at 52, 52, 53, 55, 55, 56, 57, 64, 71

55 - 64 keys