GE > PE? This used to be 1.6 buds.

Sale #1:

http://www.tf2outpost.com/trade/25559765

Sold for a Max Head ~28 keys

http://backpack.tf/profiles/76561198096014722?time=1428044400 (April 3rd)

http://backpack.tf/profiles/76561198096014722?time=1428130800 (April 4th)

Sale #2:

Sold for 23 keys

http://backpack.tf/profiles/76561198123917552?time=1432278000 (May 22nd)

http://backpack.tf/profiles/76561198123917552?time=1432364400 (May 23rd)

Was probably bought as a quicksell: http://www.tf2outpost.com/trade/25969259

Though it's hardly a quicksell when there's an active seller asking for less:

http://www.tf2outpost.com/trade/25947069 Asking 22 keys (check comments)

Sale #3:

http://www.tf2outpost.com/trade/25572144

Sold for Ghosts Fez (36.5)

http://backpack.tf/profiles/76561198098325034?time=1431500400 (May 13th)

http://backpack.tf/profiles/76561198098325034?time=1431673200 (May 15th)

This should be an easy outlier.

Support:

http://www.tf2outpost.com/trade/25241991

Sold for 21 keys

http://backpack.tf/profiles/76561198098325034?time=1425801600 (March 8th)

http://backpack.tf/profiles/76561198098325034?time=1425884400 (March 9th)