Yay, first suggestion here! Anyways, here’s the proof:

Hidden offers:

http://www.tf2outpost.com/trade/7921496 - offer of 3 ref, hidden by trade owner

http://www.tf2outpost.com/trade/7850390 - offer of 3 ref, noped by trade owner

http://www.tf2outpost.com/trade/7885974 - offer of 3.44, hidden

http://www.tf2outpost.com/trade/7739126 - offer of a key, hidden

http://www.tf2outpost.com/trade/7863879 - offer of a key, hidden

Sold:

http://www.tf2outpost.com/trade/7966692 - sold for a key

Unsold:

http://www.tf2outpost.com/trade/7850390 - selling for a key

http://www.tf2outpost.com/trade/7954110 - selling for a key

http://www.tf2outpost.com/trade/7935569 - selling for a key

http://www.tf2outpost.com/trade/7953739 - selling for 4 ref

http://www.tf2outpost.com/trade/7948095 - selling for 4.33

http://www.tf2outpost.com/trade/7926210 - selling for 4.66

http://www.tf2outpost.com/trade/7933222 - selling for 4.66

http://www.tf2outpost.com/trade/7715767 - selling for 4.77

http://www.tf2outpost.com/trade/7949383 - selling for key+ref

Pretty much shows that buyers want to pay 3 ref to a key, and sellers want to sell for a key to 4.77 ref. Most of the trades on outpost were unsold, which (plus me trying to sell mine for a while) tells me that they’re hard to sell and people don’t want to buy them unless it’s around 3 ref. Anyways, 1-1.5 keys is way too high.