http://www.tf2outpost.com/trade/20334786 Sold for Planets Bombing run, ~13 keys. see http://backpack.tf/profiles/76561198062287463?time=1402642800 and http://backpack.tf/profiles/76561198062287463?time=1402729200

http://www.tf2outpost.com/trade/18496732 Initially selling at 11 but agreed to 9 keys without haggling.

http://www.tf2outpost.com/trade/19266173 "Quicksold" for 10 keys but it seems to have taken a while.

9 keys seems a bit low and quickselly, so I'll discard it as valid proof. 10 keys, on the other hand, took at least a few weeks judging by the dates and really can't be considered a quicksell, so I'll use it as the low end.