Proof:

1) http://www.tf2outpost.com/trade/22313522

Seller: http://backpack.tf/profiles/76561198064654530?time=1409122800 => http://backpack.tf/profiles/76561198064654530?time=1409295600

Sold for Blizzardy Storm Respectless Rubber Glove + 8 keys (0.9 * 17 + 8) / 17 = 1.37

2)

Seller: http://backpack.tf/profiles/76561198032577838?time=1406358000 => http://backpack.tf/profiles/76561198032577838?time=1406530800

Buyer: http://backpack.tf/profiles/76561198064294882?time=1406271600 => http://backpack.tf/profiles/76561198064294882?time=1406358000

Bought S.Storm Reggaelator (1.6 buds) and AH Lid and 6 keys (0.3 buds) sweets with Cloud 9 Hat With No Name (3.17 buds) 3.17 - 1.6 - 0.3 = 1.27

3) http://www.tf2outpost.com/trade/20051377 (I know this trade is little outdated but still...) Sold for TW Fruit shot 0.9 * 1.3 = 1.17

This all I found.

http://www.tf2outpost.com/trade/22690430 this one is unsold for 25 keys for about 1 month so it shows that 1.5 buds doesn't sell