Sale 1:

Sold for Strange Pro. KS Awper Hand (13.5) + ~10 keys in items

No outpost

Seller: http://backpack.tf/profiles/76561198096389539#!/compare/1479254400/1479340800

Buyer: http://backpack.tf/profiles/76561198211858204#!/compare/1479254400/1479340800

X = 24

Sale 2: (Dupe)

Sold for 19 keys

http://www.tf2outpost.com/trade/28661445 - B/O of 19, seller confirms sale (legend)

Seller: http://backpack.tf/profiles/76561198031371895#!/compare/1482364800/1482451200

Buyer: http://backpack.tf/profiles/76561198070864070#!/compare/1482192000/1482451200

X = 19

Sale 3:

Sold for 15 keys in ~2 days

http://www.tf2outpost.com/trade/28622755 - B/O of ~14.7

Seller: http://backpack.tf/profiles/76561198002757046#!/compare/1479859200/1479945600

Buyer: http://backpack.tf/profiles/76561197970567963#!/compare/1479945600/1481068800

X = 15

Sellers:

20 keys:

http://www.tf2outpost.com/trade/28620601 - 2 months

http://backpack.tf/u/76561198075397782

Sales at:

15

19

24

Excluding 15, since it sold rather quickly.

24 is too high, as the seller at 20 keys Is 2 months old. Excluding 24.

Going with 19 flat.