Price is outdated. There are several unsold for 6 keys on outpost, and several have been sold at that price. Definitely time for a price change.

Sold/Selling for 6 keys

http://www.tf2outpost.com/trade/7623925 - Accepts offer of 6 keys

http://www.tf2outpost.com/trade/7874059 - Selling for 6 keys

http://www.tf2outpost.com/trade/7878397 - Selling for 6 keys

http://www.tf2outpost.com/trade/7880230 - Sold for 6 keys

Unsold for 7 keys

http://www.tf2outpost.com/trade/7899073 - Unsold for 7 keys

http://www.tf2outpost.com/trade/7724554 - Unsold for 7 keys

http://www.tf2outpost.com/trade/7892991 - Unsold for 7 keys

Impossible to sell at 7, some people (including Soundtrack) are offering 5 but not getting any reward, 6 seems like the correct price for now.