Sale 1:

Sold for 19 keys

Seller: http://backpack.tf/profiles/76561198004517334#!/compare/1492560000/1492646400

Buyer: http://backpack.tf/profiles/76561198072702865#!/compare/1492646400/1492819200

X = 19

Sale 2:

Sold with a key for Peace Sign Dragonborn (19)

No outpost

Seller: http://backpack.tf/profiles/76561198289372905#!/compare/1489795200/1489881600

Buyer: http://backpack.tf/profiles/76561198089774957#!/compare/1489881600/1489968000

X = 18

Sale 3:

Sold for 14 key + <0.5 keys in metal in ~2 days

http://www.tf2outpost.com/trade/28837605 - Deleted B/O

Seller: http://backpack.tf/profiles/76561198049149130#!/compare/1489795200/1489881600

Buyer: http://backpack.tf/profiles/76561198289372905#!/compare/1489795200/1489881600

X = 14

Sale 4:

Sold with 4 keys + ~1 key in items for Max's Head (18 at the time) in ~3 days

http://www.tf2outpost.com/trade/28839583 - B/O of 17.5

Seller: http://backpack.tf/profiles/76561198089774957#!/compare/1489968000/1490227200

Buyer: http://backpack.tf/profiles/76561198031371895#!/compare/1490054400/1490227200

X = 13

Sale 5:

Bulk? for Mallard Grimm

Seller: http://backpack.tf/profiles/76561198116164243#!/compare/1489536000/1489708800

Buyer: http://backpack.tf/profiles/76561198049149130#!/compare/1489622400/1489708800

Seller at 20 for a month on the classifieds

18-19