The current price is outdated. People successfully selling it for 5, even for 6 keys. 4 keys now seems like a quicksell price. Proof is below.

Sellers:

http://www.tf2outpost.com/trade/8555667 - 7.5 keys, 2 days, unsold, got a 7 keys offer

http://www.tf2outpost.com/trade/8584347 - no B/O, got a 7 keys offer

You may ask - so why you didn't put 7 keys as the high-end of the price? This guy made few 7 keys quickoffers, but then bought it for 5 keys (this one - http://www.tf2outpost.com/trade/8502578)

http://www.tf2outpost.com/trade/8502182 - 6 keys, sold

http://www.tf2outpost.com/trade/8478496 - 6 keys, sold

http://www.tf2outpost.com/trade/8332760 - sold for 5 keys + 2 ToD tickets



http://www.tf2outpost.com/trade/8483431 - 5 keys, sold

http://www.tf2outpost.com/trade/8502578 - 5 keys, sold

http://www.tf2outpost.com/trade/8577273 - 5 keys, sold

http://www.tf2outpost.com/trade/8597874 - 5 keys, 18 hours, no takers

http://www.tf2outpost.com/trade/8529025 - 5 keys, 3 days, unsold

Buyers:

http://tf2tp.com/trade.php?trade=9134214 - ~6.5 keys in items, bought a golden one

http://www.tf2outpost.com/trade/8604098 - ~4.5 keys in items, no takers

http://www.tf2outpost.com/trade/8182300 - 4 keys, 2 weeks, no takers

http://www.tf2outpost.com/trade/8359753 - 4 keys, 1 week, no takers

http://www.tf2outpost.com/trade/8498587 - 4 keys, 4 days, no takers

http://www.tf2outpost.com/trade/8604098 - 4 keys

http://www.tf2outpost.com/trade/8246040 - 4 keys, bought one