Adding sweets for sweets is completely logical.

Sold with ~1 Key in Sweets for a Disco Beat Down Bone Dome(20 Keys), a Kill-a-Watt Ol' Geezer(15 Keys) and ~1 Key in Sweets(35 Keys total)

http://backpack.tf/profiles/76561198087051898/#!/compare/1456992000/1457078400

Sold for a Molten Mallard Virtual Reality Headset(35 Keys) and ~2 Keys in Sweets(37 Keys total)

http://backpack.tf/profiles/76561198085304366/#!/compare/1457078400/1457251200

http://backpack.tf/profiles/76561198101610113/#!/compare/1457164800/1457251200

Sold with ~1.5 Keys in Sweets for an Amaranthine Helmet Without A Home(35.5 Keys) and ~2 Keys in Sweets(36 Keys total)(B/O was 35)

http://backpack.tf/profiles/76561198085304366/#!/compare/1457424000/1457510400

http://www.tf2outpost.com/trade/27930288

Sales seem to fit, 35-37 Keys should be fine.

Additional Proof/Counter-Proof/Constructive Criticism/Feedback is always appreciated.