Sale 1:

Sold for 12 keys

http://www.tf2outpost.com/trade/29326020 - B/O of 12

Seller: https://backpack.tf/profiles/76561198106233311#!/compare/1503619200/1503705600

Buyer: https://backpack.tf/profiles/76561198027150240#!/compare/1503705600/1505433600

X = 12

Sale 2:

Sold for 12 keys (IDs match)

http://www.tf2outpost.com/trade/29381196 - B/O of 12

Seller: https://backpack.tf/profiles/76561198052852471#!/compare/1506556800/1506643200

Buyer: https://backpack.tf/profiles/76561198367946947#!/compare/1505001600/1506729600

X = 12

Sale 3:

Quicksold for 11 keys

http://www.tf2outpost.com/trade/29369804 - B/O of 11, sold in a day

Seller: https://backpack.tf/profiles/76561198027150240#!/compare/1505520000/1505606400

Buyer: https://backpack.tf/profiles/76561198414604584#!/compare/1505606400/1505865600

X = 11

Sale 4:

Bulk for DBD Bot Dogger

Seller: https://backpack.tf/profiles/76561198071012049#!/compare/1502409600/1502582400

Buyer: https://backpack.tf/profiles/76561198106233311#!/compare/1502496000/1502582400

Sale 5:

Bulk for Miami Jumper’s Jeepcap

Seller: https://backpack.tf/profiles/76561198367946947#!/compare/1506729600/1506902400

Buyer: https://backpack.tf/profiles/76561198024925599#!/compare/1506643200/1506729600

https://i.imgur.com/aQTOUb3.png

Sellers:

13 keys:

https://i.imgur.com/aQTOUb3.png - 6 days

https://i.imgur.com/hKggBJc.png - 1 day

15 keys:

http://www.tf2outpost.com/trade/29386309 - 4 days

Sales at:

11

12 (2x)

11 quicksold, excluding 11.

Going with 12 flat.