Sale #1:

Sold for 28 keys (matching id's) http://i.imgur.com/408oRgr.png

http://backpack.tf/profiles/76561198050557276#!/compare/1458716400/1458864000

Sale #2:

Sold for Pro KS SF Sniper Rifle (~18)

http://backpack.tf/profiles/76561198190579477#!/compare/1462406400/1462838400

Probably an outlier.

Sale #3:

Sold with Blizz Front Runner for PE Milkman - not usable

http://backpack.tf/profiles/76561198013066994#!/compare/1458457200/1458543600

Sale #4:

Sold for 32 keys

https://backpack.tf/profiles/76561198017078036#!/compare/1459900800/1460505600

Sale #4:

Sold for Power Surge Bubble Pipe (used to price Bubble)

http://backpack.tf/profiles/76561198030630425#!/compare/1460592000/1460678400

Sale #5:

http://www.tf2outpost.com/trade/28031237 Quick-sold for 24 keys

http://backpack.tf/profiles/76561198276725194#!/compare/1459468800/1459555200

http://backpack.tf/profiles/76561198030630425#!/compare/1459468800/1459555200

Sale #6:

Unclear

http://backpack.tf/profiles/76561198276725194#!/compare/1459123200/1459209600

http://backpack.tf/profiles/76561198182399626#!/compare/1459123200/1459209600

Sellers in classifieds at 28-30 keys:

http://i.imgur.com/5X3YhRO.png

Sales are 18, 24, 28, and 32. 24 sale happened within hours, range should be 28-32 keys.