Sale 1:

Sold for Smoking Towering Pillar of Hats (20) + 10 keys

http://www.tf2outpost.com/trade/28566576 - Deleted B/O, relisted from here: http://www.tf2outpost.com/trade/28564912 - B/O of 30

Seller: http://backpack.tf/profiles/76561198010082723#!/compare/1477526400/1477699200

Buyer: http://backpack.tf/profiles/76561198196131666#!/compare/1477440000/1477699200

X = 30

Sale 2:

Sold with 1 key + 2 ToD Tickets (1) for Cloud 9 Noble (24) in about a day

http://www.tf2outpost.com/trade/28570687 - B/O of 29

Seller: http://backpack.tf/profiles/76561198196131666#!/compare/1477699200/1477785600

Buyer: http://backpack.tf/profiles/76561198004517334#!/compare/1477699200/1477785600

X = 22

Sellers:

28 keys:

http://i.imgur.com/gifbIgb.png - 21 days

http://backpack.tf/u/76561198004517334

http://www.tf2outpost.com/trade/28574285

30 keys:

http://i.imgur.com/pEFajC4.png

http://backpack.tf/u/76561198000583758

http://www.tf2outpost.com/trade/28634618 - 4 days

http://backpack.tf/u/76561198047433991

http://www.tf2outpost.com/trade/28632906

40 keys:

http://i.imgur.com/TFixaMD.png - 3 months

http://backpack.tf/u/76561198090956917

Sales at:

22

30

Given that the sale at 22 looks pretty low, and sold in about a day, I’m going to exclude this sale.

Seller at 28 is 3 weeks old.

Going with 28-30.