Didn't change much after 2 years :P

Sale 1:

Sold for 12 keys

12 keys

http://backpack.tf/profiles/76561198021221797?time=1431759600 (May 16th)

http://backpack.tf/profiles/76561198021221797?time=1431846000 (May 17th)

Sale 2:

Sold with 3 keys for a Smoking Towering Pillar of Hats

(17*0.9) - 3 = 12.3 rounding to 12 keys

http://backpack.tf/profiles/76561198051339270?time=1430550000 (May 2nd)

http://backpack.tf/profiles/76561198051339270?time=1430722800 (May 4th)

Sale 3: (outlier)

Sold for a Prof. Australium Force-A-Nature

Comes out to around 20 keys based on the SCM

http://backpack.tf/profiles/76561198089471744?time=1430550000 (May 2nd)

http://backpack.tf/profiles/76561198089471744?time=1431154800 (May 9th)

Conclusion:

2 sales at 12 keys, taking the final price at 12 keys.