Sellers:

http://www.tf2outpost.com/trade/29197987 - b/o: 11 keys (8 days)

Sold:

https://marketplace.tf/items/100;5;u59 - sold for $28 = 13 keys, $28.02 = 13 keys, $27.90 = 13 keys

http://backpack.tf/profiles/76561197960328421#!/compare/1495756800/1495843200 - sold for Orbiting Planets Elf Esteem (11) + 1 key + sweets (1) = 13 keys

http://backpack.tf/profiles/76561197960328421#!/compare/1494460800/1494547200 - ?

http://backpack.tf/profiles/76561198108021386#!/compare/1494460800/1494547200 - ?

http://www.tf2outpost.com/trade/28894697

http://backpack.tf/profiles/76561198106690065#!/compare/1492992000/1493078400 - bulk for keys

http://backpack.tf/profiles/76561198200723198#!/compare/1491955200/1492387200 - ?

http://backpack.tf/profiles/76561198199710042#!/compare/1491091200/1491264000 - ?

http://www.tf2outpost.com/trade/28853477

http://backpack.tf/profiles/76561198315072848#!/compare/1490918400/1491004800 - sold for 10 keys (quicksold)

http://backpack.tf/profiles/76561198084668327#!/compare/1490572800/1490745600

http://backpack.tf/profiles/76561198315072848#!/compare/1474502400/1490745600 - ?

http://www.tf2outpost.com/trade/28818089

http://backpack.tf/profiles/76561198167082530#!/compare/1490486400/1490572800

http://backpack.tf/profiles/76561198216133209#!/compare/1490400000/1490486400 - ?

http://backpack.tf/profiles/76561198138945248#!/compare/1495584000/1495929600

http://backpack.tf/profiles/76561198254324824#!/compare/1495756800/1495843200 - ?

http://www.tf2outpost.com/trade/29197325

http://backpack.tf/profiles/76561198140964079#!/compare/1495584000/1495670400 - sold for 10 keys (quicksold)

http://backpack.tf/profiles/76561198271948037#!/compare/1495584000/1495670400 - sold for 10 keys (low)

http://backpack.tf/profiles/76561198133931315#!/compare/1492214400/1492300800 - ?

Conclusion:

sales at 10, 10, 10, 13, 13, 13, 13

seller at 11

taking 11-13 keys