The Roarin' 20s.

http://backpack.tf/item/3830442531

Sale 1) Sold for a Stormy Storm Berlin Brain Bowl (30 Keys) + ~3 Keys of Items

http://backpack.tf/profiles/76561198073553007#!/compare/1493856000/1493942400

http://www.tf2outpost.com/trade/28909867 - Capped by the Buyout of 27 Keys

Sale 2) Sold for 26 Keys

http://backpack.tf/profiles/76561198043936328#!/compare/1496016000/1496102400

http://backpack.tf/item/3467969746

Sale 3) Sold + 5 Keys for a Duped Blizzardy Storm Modest Pile of Hat (28 Keys)

http://backpack.tf/profiles/76561198271088156#!/compare/1491696000/1491868800

28 - 3 = 25 Keys

Modest Mini

http://backpack.tf/profiles/76561198063640894#!/compare/1493596800/1493683200 - Sold for 31 Keys

http://backpack.tf/profiles/76561198156754433#!/compare/1495152000/1495238400 - Sold + Pool Party (~3 Keys) for a DBD Merryweather (28 Keys)

http://backpack.tf/item/2181783142

Sale 4) Sold for 21 Keys

http://backpack.tf/profiles/76561198073553007#!/compare/1492214400/1492300800

Sale 5) Sold for 21 Keys

http://backpack.tf/profiles/76561198128606394#!/compare/1492646400/1492732800

Sale 6) Sold for 22 Keys + ~1 Keys of Items

http://backpack.tf/profiles/76561198050518375#!/compare/1492992000/1493078400

22 + 1 = 23 Keys

Sale 7) Sold for 23 Keys + ~2 Keys of Items

http://backpack.tf/profiles/76561198310901512#!/compare/1493251200/1493337600 - Buyer's Backapck

23 + 2 = 25 Keys

Sale 8) Sold for a Blizzardy Storm Master's Yellow Belt (22.5 Keys)

http://backpack.tf/profiles/76561198090614429#!/compare/1494547200/1494633600 - Buyer's Backpack

Rounding to 23 Keys

Sale 9) Sold for a Terror-Watt Backwards Ballcap (33 Keys)

http://backpack.tf/profiles/76561198174209565#!/compare/1496275200/1496361600

http://www.tf2outpost.com/trade/29197628 - Capped by the Buyout of 30 Keys

High Outlier.