Ghostpotters.

http://backpack.tf/item/1223089200

Sale 1) Sold for a Neutron Star Toadstool Topper (28.5 Keys)

http://backpack.tf/profiles/76561198356389238#!/compare/1490140800/1490227200

http://www.tf2outpost.com/trade/28843315 - Capped by the Buyout of 28 Keys

Sale 2) Sold + ~3 Keys of Items for a Starstorm Slumber Nasty Norsemann (23 Keys)

http://backpack.tf/profiles/76561198176521109#!/compare/1493078400/1493251200

23 - 3 = 20 Keys

Sale 3) Sold for a Circling Heart Birdcage (27 Keys) + 3 Keys

http://backpack.tf/profiles/76561198127333582#!/compare/1493078400/1493164800

27 + 3 = 30 Keys

Sale 4) Sold for an Orbiting Planets Towering Pillar of Hats + 12 Keys

http://backpack.tf/profiles/76561198263344996#!/compare/1493424000/1493683200

http://www.tf2outpost.com/trade/28900716 - Capped by the Buyout of 34 Keys

Sale 5) Sold for a Professional Killstreak Australium Ambasador (~16 Keys) + ~5 Keys of Items

http://backpack.tf/profiles/76561198229334060#!/compare/1496534400/1496620800

16 + 5 = 21 Keys

Going conservative with 28 - 34 Keys.