Sale 1:

Sold for 20 keys

Seller: https://backpack.tf/profiles/76561198080179568#!/compare/1510099200/1510185600

Buyer: https://backpack.tf/profiles/76561198197338561#!/compare/1510099200/1510185600

X = 20

Sale 2:

Sold for Insomnia Airdog (15.5) + ~4 keys in items

http://www.tf2outpost.com/trade/29390902 - No B/O

Seller: https://backpack.tf/profiles/76561198101327173#!/compare/1507075200/1507334400

Buyer: https://backpack.tf/profiles/76561198052042939#!/compare/1507161600/1507334400

X = 20

Sale 3:

Sold for 20 keys

Seller: https://backpack.tf/profiles/76561198128276213#!/compare/1510876800/1510963200

Buyer: https://backpack.tf/profiles/76561198026509644#!/compare/1510963200/1511222400

X = 20

Sale 4:

Sold for Vivid Handyman’s Handle (Suggestion at 15) + 4 keys + cheap items

http://www.tf2outpost.com/trade/29379187 - Deleted B/O

Seller: https://backpack.tf/profiles/76561198219681600#!/compare/1506211200/1506297600

Buyer: https://backpack.tf/profiles/76561198090147535#!/compare/1506038400/1506297600

X = 19

Sale 5:

Sold for 18 keys

Seller: https://backpack.tf/profiles/76561198394877897#!/compare/1512000000/1512086400

Buyer: https://backpack.tf/profiles/76561198022806102#!/compare/1511913600/1512086400

X = 18

Sale 6:

Sold for 18 keys

Seller: https://backpack.tf/profiles/76561198022806102#!/compare/1512432000/1512518400

Buyer: https://backpack.tf/profiles/76561198155981570#!/compare/1512432000/1512518400

X = 18

Sale 7:

Sold for 18 keys

Seller: https://backpack.tf/profiles/76561198274517895#!/compare/1506556800/1506643200

Buyer: https://backpack.tf/profiles/76561198141079760#!/compare/1506556800/1506643200

X = 18

Sale 8:

Sold for 17 keys + cheap taunts

Seller: https://backpack.tf/profiles/76561198075532147#!/compare/1508112000/1508371200

Buyer: https://backpack.tf/profiles/76561198066207210#!/compare/1508284800/1508371200

X = 17

Sale 9:

Sold for 17 keys + 17 ref

Seller: https://backpack.tf/profiles/76561198066207210#!/compare/1510790400/1510876800

Buyer: https://backpack.tf/profiles/76561198128276213#!/compare/1510790400/1510876800

X = 17

Sale 10:

Bulk for Aces Pyromancer

Seller: https://backpack.tf/profiles/76561198068090261#!/compare/1506816000/1506902400

Buyer: https://backpack.tf/profiles/76561198075532147#!/compare/1506816000/1506902400

Sale 11:

Bulk for Green Energy Festive Tree

Seller: https://backpack.tf/profiles/76561197997810328#!/compare/1512086400/1512172800

Buyer: https://backpack.tf/profiles/76561198208150535#!/compare/1512086400/1512172800

Sale 12:

Sold for Cloud 9 Noble Nickel + ~1 key in items

No outpost

Seller: https://backpack.tf/profiles/76561198141079760#!/compare/1509062400/1509235200

Buyer: https://backpack.tf/profiles/76561198331590002#!/compare/1508457600/1509235200

Not using without a B/O.

Sale 13:

Bulk for Purple Energy Coldsnap

Seller: https://backpack.tf/profiles/76561198331590002#!/compare/1510531200/1510617600

Buyer: https://backpack.tf/profiles/76561198049149130#!/compare/1510358400/1510617600

Vivid Handle:

https://backpack.tf/suggestion/5a2cd576cf6c7576ba0dc993

Sellers:

19 keys:

https://i.imgur.com/Ja5CHYi.png - young

~19.5 keys:

https://i.imgur.com/NnrMdOM.png - 17 days

https://i.imgur.com/E9Lf47n.png - 4 days

Sales at:

17 (2x)

18 (3x)

19

20 (3x)

Going with 17-20.