Using last month.

Sale 1:

Sold for $50 on Marketplace.tf

https://marketplace.tf/items/30922;5;u3007

50/1.98 = ~25.25252525

X = 25

Sale 2:

Sold for Skill Gotten Gains Meet the Medic (Mini at 7.25 below) + 6 keys

No outpost

Seller: https://backpack.tf/profiles/76561197972383519#!/compare/1525219200/1525305600

Buyer: https://backpack.tf/profiles/76561198066516927#!/compare/1525305600/1525564800

X = 13

Sale 3:

Sold for 12 keys

Seller: https://backpack.tf/profiles/76561198305676157#!/compare/1524009600/1524096000 - Near ID: 6789341623

Buyer: https://backpack.tf/profiles/76561198064374638#!/compare/1523750400/1524096000

Untraceable (apart from key histories below), but bot.tf confirms: https://i.imgur.com/fJbflPQ.png

X = 12

Key histories (Buyer’s backpack wasn’t scanned when they had the keys):

https://backpack.tf/item/6789341638

https://backpack.tf/item/6789341654

https://backpack.tf/item/6789341673

https://backpack.tf/item/6789341690

https://backpack.tf/item/6789341703

https://backpack.tf/item/6789341728

https://backpack.tf/item/6789341741

https://backpack.tf/item/6789341771

https://backpack.tf/item/6789341787

https://backpack.tf/item/6789341814

https://backpack.tf/item/6789341844

https://backpack.tf/item/6789341862

Sale 4:

Sold to a bot for 11 keys

Seller: https://backpack.tf/profiles/76561198082378911#!/compare/1523318400/1523404800

Buyer: https://backpack.tf/profiles/76561198305676157#!/compare/1523232000/1523318400

9 keys went towards the DBD Swagman before the seller’s backpack was scanned:

https://backpack.tf/profiles/76561198313538268#!/compare/1523145600/1523318400 (last 9 keys)

Bot.tf confirms: https://i.imgur.com/fJbflPQ.png

X = 11

Sale 5:

Quicksold for 11 keys (ID’s match)

Seller: https://backpack.tf/profiles/76561198305676157#!/compare/1523836800/1523923200

Buyer: https://backpack.tf/profiles/76561198067200487#!/compare/1523750400/1523923200

Bot.tf confirms: https://i.imgur.com/fJbflPQ.png

X = 11

Skill Gotten Gains Meet the Medic:

https://backpack.tf/suggestion/5af2baf3cf6c7569d06b3d5e

No current sellers.

Sales at:

11 (2x)

12

13

25

25 is a large outlier, excluding.

11 either quicksold or went to a bot, excluding 11.

Going with 12-13.