Proof:

Offers:

http://www.tf2outpost.com/trade/18027997 - Selling for 1.6 keys, had a retracted offer (he says he bought 2 for 3 keys, 1.5 each), has another interested buyer

http://www.tf2outpost.com/trade/8702257 - 2 keys

Sales:

http://www.tf2outpost.com/trade/18342789 - Sold for 1.5 keys in less than 3 hours

http://imgur.com/ZmvE9T7 - Sold for 1.6 keys

http://bazaar.tf/trade/709297 - Sold for 2 keys

http://www.tf2outpost.com/trade/18197515 - Claims he sold 4, has an added comment and he has a Strange Degreaser with only 7 reflected projectiles, probably sold

http://www.tf2outpost.com/trade/18345929 - Sold for 2 keys in 1 hour

Outpost has literally less than a page

Most trades are done through Steam Community Market

There are recent trades at ~1.5 - 1.6 and also some B/O's around there

1.5 and 1.6 are probably a quicksell but with such a small market I don't think it's avoidable

Not much proof can be found, keep that in mind

If you have any doubt, go search outpost yourself