Shocking!

Sale 1:

https://backpack.tf/profiles/76561198337734785#!/compare/1542931200/1543017600

https://backpack.tf/profiles/76561198442218271#!/compare/1542758400/1543017600

= 8 keys + 18 refined metal

≈ 8.5 keys

Sale 2:

https://backpack.tf/profiles/76561198442218271#!/compare/1543622400/1543795200

https://backpack.tf/profiles/76561198412224224#!/compare/1543622400/1543708800

= 8 keys

Sale 3:

https://backpack.tf/profiles/76561198412224224#!/compare/1543708800/1543795200

https://backpack.tf/profiles/76561198043806938#!/compare/1543708800/1543795200

Nothing

Sale 4:

https://backpack.tf/profiles/76561198043806938#!/compare/1543968000/1544054400

https://backpack.tf/profiles/76561198412224224#!/compare/1543795200/1544054400

Nothing

Sale 5:

https://backpack.tf/profiles/76561198412224224#!/compare/1544054400/1544140800

https://backpack.tf/profiles/76561198338424715#!/compare/1543968000/1544140800

= Cloud 9 Base Metal Billycock (13 keys ~ https://backpack.tf/suggestion/5c44a84644325a58b058b485)

= 13 keys

Sale 6:

https://backpack.tf/profiles/76561198335791307#!/compare/1544140800/1544227200

https://backpack.tf/profiles/76561198338424715#!/compare/1544140800/1544227200

Unclear

Sale 7:

https://backpack.tf/profiles/76561198250067726#!/compare/1547164800/1547942400

https://backpack.tf/profiles/76561198335791307#!/compare/1547856000/1547942400

Unclear

Sale 8:

https://backpack.tf/profiles/76561198312583107#!/compare/1548374400/1548460800

https://backpack.tf/profiles/76561198250067726#!/compare/1548115200/1548633600

= 7 keys + 20 refined metal

≈ 7.5 keys

Sale 9:

https://backpack.tf/profiles/76561198312583107#!/compare/1550275200/1550361600

https://backpack.tf/profiles/76561198101516820#!/compare/1550275200/1550361600

= 9 keys +16 refined metal + Taunt: Rancho Relaxo (22.5 refined metal) + The Pilotka (1.67 refined metal) + Taunt: Conga (33.83 refined metal) + Strange Bazaar Bargain (18.61 refined metal)

= 9 keys + 92.61 refined metal

≈ 11 keys

(Note: despite the comparison links differing in contents, all items the aforementioned items were traded at the same time as one another. Hence, I came to the conclusion that they were all part of the deal).

Summary of sales (keys): 8, 8.5, 13, 7.5, 11

Excluding: 7.5 (close to buyers), 13 (there's an unsold at 9 keys for 1 month ~ recommended by Wrein, thank you!)

Concluding range: 8-11 keys