Sale 1:

Sold with 4 keys for Spec. KS Aussie Scattergun (24)

http://www.tf2outpost.com/trade/29335606 - No B/O

Seller: https://backpack.tf/profiles/76561198298210084#!/compare/1503187200/1503273600

Buyer: https://backpack.tf/profiles/76561198254015856#!/compare/1503187200/1503273600

X = 20

Sale 2:

Sold for 19 keys + 5 ref

http://www.tf2outpost.com/trade/29337947 - B/O of 20

Seller: https://backpack.tf/profiles/76561198254015856#!/compare/1503446400/1503532800

Buyer: https://backpack.tf/profiles/76561198163549413#!/compare/1503360000/1503532800

X = 19

Sale 3:

Sold for 19 keys + <0.5 keys in metal/items

http://www.tf2outpost.com/trade/29359541 - B/O of “19 + sweets”, was re-listed several times

Seller: https://backpack.tf/profiles/76561198163549413#!/compare/1504656000/1504742400

Buyer: https://backpack.tf/profiles/76561198103017176#!/compare/1504569600/1504742400

X = 19

Sale 4:

Bulk for Ooze Yellow Belt

Seller: https://backpack.tf/profiles/76561198100007274#!/compare/1499212800/1499558400

Buyer: https://backpack.tf/profiles/76561198061376237#!/compare/1498867200/1499299200

Sale 5:

Bulk for Peace Sign Gibus

Seller: https://backpack.tf/profiles/76561198044034074#!/compare/1502064000/1502150400

Buyer: https://backpack.tf/profiles/76561198087402437#!/compare/1502064000/1502150400

Sale 6:

Bulk for something

Seller: https://backpack.tf/profiles/76561198062329277#!/compare/1503014400/1503100800

Buyer: https://backpack.tf/profiles/76561198298210084#!/compare/1503014400/1503100800

Sellers:

19 keys:

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

26 keys:

https://i.imgur.com/dPlxPSM.png - 2 days

27 keys:

https://i.imgur.com/2igl5WQ.png - 2 months

Who knows:

http://www.tf2outpost.com/trade/29339055 - 2 weeks

Sales at:

19 (2x)

20

Going with 19-20.