There is not much demand for the untradable ones. Proof below:

Selling for 0.66 ref:

http://www.tf2outpost.com/trade/8512208

http://www.tf2outpost.com/trade/8628925

Looking for 0.33 ref:

http://www.tf2outpost.com/trade/8635409

Being offered 1 ref:

http://www.tf2outpost.com/trade/4902323

Being offered items worth 0.33 ref:

http://www.tf2outpost.com/trade/8310521 (accepted)

Being offered 0.66 ref:

http://www.tf2outpost.com/trade/8488411

Being offered 1.33 ref in items:

http://www.tf2outpost.com/trade/8510291 (strange direct hit + 2 rec + wrap which he needs time to obtain o.o)

Although there were offers of 1 ref and also 1.33 ref, however, this item can be obtained for 0.33 ref and those selling for 0.66 ref hasn't sold theirs. It is easy to obtain this at 0.33-0.66 ref.