Sale 1:

Sold for 20 keys

No outpost

Seller: http://backpack.tf/profiles/76561198044180589#!/compare/1463443200/1463529600

Buyer: http://backpack.tf/profiles/76561197972711665#!/compare/1463270400/1463529600

X = 20

Sale 2:

Sold for 20 keys

http://www.tf2outpost.com/trade/28187594 - B/O of 21, Seller confirms sale (Legend)

Seller: http://backpack.tf/profiles/76561198047887998#!/compare/1463788800/1463875200

Buyer: http://backpack.tf/profiles/76561198119242349#!/compare/1463788800/1463875200

X = 20

Sale 3:

Sold for Lantern Dead Cone + 3 keys in items

http://www.tf2outpost.com/trade/28276676 - B/O of 20

Seller: http://backpack.tf/profiles/76561198020674825#!/compare/1466467200/1466553600

Buyer: http://backpack.tf/profiles/76561198211717085#!/compare/1466640000/1466899200

X = 20

Sale 4:

Sold for Pro. KS Collector’s Festive Flare Gun + 2 keys in items

http://www.tf2outpost.com/trade/28216083 - B/O of 20

Seller: http://backpack.tf/profiles/76561198056637705#!/compare/1466121600/1466380800

Buyer: http://backpack.tf/profiles/76561198074726834#!/compare/1466380800/1466553600

No idea what to value the festive flare gun at, there are no recent sales on the SCM. However, non-ks ones are 18 keys. This should be enough to cap at the B/O

X = 20 (Capped by B/O)

Sale 5:

Sold for Spec. KS Aussie Stickybomb Launcher (~18 at the time) + 1 key in items

http://www.tf2outpost.com/trade/27860205 - No B/O

Seller: http://backpack.tf/profiles/76561198094693231#!/compare/1463702400/1463788800

Buyer: http://backpack.tf/profiles/76561198047887998#!/compare/1463702400/1463788800

X = 19

Sale 6:

Sold for Peace Sign Hotrod + 1 key

No outpost

Seller: http://backpack.tf/profiles/76561198048851745#!/compare/1462320000/1462406400

Buyer: http://backpack.tf/profiles/76561198064709487#!/compare/1462406400/1462492800

X = 18

Sale 7:

Quicksold for 15 keys

No outpost

Seller: http://backpack.tf/profiles/76561197999873164#!/compare/1466812800/1466899200

Buyer: http://backpack.tf/profiles/76561198043936328#!/compare/1466812800/1466899200

X = 15

Sellers:

20 keys:

http://puu.sh/pNFUs/e99008ca0c.png - 4 days

Sales at:

15

18

19

20 (4x)

15 is an outlier

Going with 18-20