Using the last 30 days

Bot.tf sales:

https://i.imgur.com/HCqYM0x.png (providing compare links for ones that could be properly identified)

Bought:

7 keys

https://backpack.tf/profiles/76561198232041512#!/compare/1521158400/1521244800

https://backpack.tf/profiles/76561198344933095#!/compare/1521244800/1522627200

6 keys + 1 ref (2x, 1 traceable)

https://backpack.tf/profiles/76561198195151562#!/compare/1519344000/1522281600

https://backpack.tf/profiles/76561198305676157#!/compare/1522195200/1522281600

6 keys

X = 7

X = 6 (3x)

Sold:

6 keys + 18 ref

https://backpack.tf/profiles/76561198305676157#!/compare/1522108800/1522195200

https://backpack.tf/profiles/76561198074625962#!/compare/1522108800/1522195200

6 keys + 17 ref

https://backpack.tf/profiles/76561198357046243#!/compare/1521849600/1521936000

https://backpack.tf/profiles/76561198258042183#!/compare/1521590400/1521936000

9 keys + 18 ref

X = 7 (2x)

X = 10

Marketplace.tf sales:

https://marketplace.tf/items/1119;5;u3005

$22.99 and $20

20/1.97 = ~10.2

22.99/1.98 = ~11.6

X = 10

X = 12

Regular sales:

Sale 1:

Sold for 6 keys + 20 ref

Seller: https://backpack.tf/profiles/76561198002757046#!/compare/1522454400/1522540800

Buyer: https://backpack.tf/profiles/76561198103180104#!/compare/1522454400/1522540800

X = 7

Sale 2:

Bulk for stuff

Seller: https://backpack.tf/profiles/76561198155082343#!/compare/1520035200/1520121600

Buyer: https://backpack.tf/profiles/76561198128213644#!/compare/1520035200/1520121600

Sale 3:

Bulk for Death at Dusk Killer’s Kabuto

Seller: https://backpack.tf/profiles/76561198128213644#!/compare/1521072000/1521244800

Buyer: https://backpack.tf/profiles/76561198232041512#!/compare/1521158400/1521244800

Sale 4:

Bulk for Time Warp Plug-in Prospector

Seller: https://backpack.tf/profiles/76561198257062729#!/compare/1520380800/1520985600

Buyer: https://backpack.tf/profiles/76561198114545227#!/compare/1520899200/1520985600

Sellers:

~6.55 keys:

https://i.imgur.com/f5v1lBC.png - young

https://backpack.tf/item/2874382804

8 keys:

https://i.imgur.com/H8mxuMN.png - 12 days

10 keys:

https://i.imgur.com/vVKYyN6.png

https://backpack.tf/item/4418269288

18 keys:

https://i.imgur.com/kGQQoeg.png

https://backpack.tf/item/2868184184

Sales at:

6 (3x)

7 (4x)

10 (2x)

12

The sales at 10 and 12 seem pretty high compared to sellers, and some of them were marketplace.tf sales which turn out to be pretty high anyways. Excluding 10 and 12.

Quickbuyer at 6, but most of the sales at 7 were closer to 6.5 keys, and the current seller at 6.5 keys shows that a flat price of 7 would be too high.

Going with 6-7.