Why do Grimms often sell for other Grimms .-.

Sale 1

http://www.tf2outpost.com/trade/26167262 Sold for DBD Grimm + 5 keys

B/O for Searing was 30

X = 26*0.9 + 5

X = 28

DBD http://backpack.tf/item/2193262302

Searing http://backpack.tf/item/3387925249

Keys https://gyazo.com/56397d4891703cb5bf5547bbb5f667f4 http://backpack.tf/profiles/76561198068404730?time=1434610800&compare=1434524400

Mini for DBD

http://backpack.tf/vote/id/55e571bfdea9e96f238b45f0 26 keys, using 26

Sale 2

http://www.tf2outpost.com/trade/26231739 Sold for P. Fetti Grimm + 8 keys + 5.5 in sweets

B/O for Searing was 35

P. Fetti had no trade, clearly offered

X = 18.5*0.9 + 8 + 5.5*0.9

X = 30

P. Fetti http://backpack.tf/item/3499427553

Searing http://backpack.tf/item/3387925249

Keys and sweets https://gyazo.com/056ca3aac05260d0211e313d8b9b13ea

Mini for P. Fetti

http://backpack.tf/vote/id/55e57d65ba8d88df1f8b45d3 18.5 keys, using 18.5