Sale 1:

Sold for Circling Heart Big Elfin Deal (28)

No outpost

Seller: http://backpack.tf/profiles/76561198026369390#!/compare/1490400000/1490486400

Buyer: http://backpack.tf/profiles/76561198086149991#!/compare/1490313600/1490400000

X = 28

Sale 2:

Sold for Miami Nights Airdog (26.5) + 1 key

http://www.tf2outpost.com/trade/28771451 - B/O of 23

Seller: http://backpack.tf/profiles/76561198153806405#!/compare/1486771200/1486857600

Buyer: http://backpack.tf/profiles/76561198054920750#!/compare/1486339200/1486857600

X = 23 (Capped by B/O)

Sale 3:

Sold for 22 keys

No outpost

Seller: http://backpack.tf/profiles/76561198108148076#!/compare/1486512000/1486598400

Buyer: http://backpack.tf/profiles/76561198153806405#!/compare/1486512000/1486598400

X = 22

Sale 4:

Quicksold for 22 keys

http://www.tf2outpost.com/trade/28853109 - B/O of 23

Seller: http://backpack.tf/profiles/76561198202369941#!/compare/1490745600/1490832000

Buyer: http://backpack.tf/profiles/76561198018653729#!/compare/1490745600/1490832000

X = 22

Sale 5:

Sold for 21 keys

No outpost

Seller: http://backpack.tf/profiles/76561198086149991#!/compare/1490745600/1490832000

Buyer: http://backpack.tf/profiles/76561198202369941#!/compare/1490745600/1490832000

X = 21

Sellers:

23 keys:

http://i.imgur.com/0QCVXCz.png - listed for 32 here

http://backpack.tf/u/76561198083894166

http://www.tf2outpost.com/trade/28854877

Sales at:

21

22 (2x)

23

28

One of the sales at 22 quicksold. Excluding 22 and below.

Going with 23-28.