Proof below.

Having absolutely no demand for my clean one, decided to do this suggestion. I don't get why anyone would pay more than 2 ref for this thing you can hardly see.

http://backpack.tf/classifieds/search/id/52054470ba25365077000008

Classifieds currently only have one selling for 2.11 ref.

Just 1 page on Outpost.

Sellers below 2.33 ref:

http://www.tf2outpost.com/trade/13663493 2 ref, 2 days

http://www.tf2outpost.com/trade/13690152 2 ref, 1 day, same as below

http://bazaar.tf/trade/361834 2 ref, 1 day

http://www.tf2outpost.com/trade/13691095 2 ref sold

http://www.tf2outpost.com/trade/13686996 2 ref sold, http://puu.sh/44BaI.jpg

http://www.tf2outpost.com/trade/13734039 2.11 ref sold

Unsolds at 2.33 ref:

http://www.tf2outpost.com/trade/13347535 2 weeks

http://www.tf2outpost.com/trade/13690152 1 week

http://www.tf2outpost.com/trade/13690152 bp.tf prices, 1 week

http://www.tf2outpost.com/trade/13681525 2 days

http://www.tf2outpost.com/trade/13730683 6 hours, young

Notable selling trades:

http://www.tf2outpost.com/trade/13494235 2.66 ref, no offers, 1 week

Conclusion: Very few trades selling dirty ones and no demand. I mean, you can't even see it really. Quite a few sellers below 2.33 ref, some unsold, but I'm still seeing a few solds for 2.33 ref. However, below 2.33 ref is very possible, hence the range.