no offers of 20 keys anywhere

I bought it for 15 keys and sold it to OP for ap-sap + 6 keys :p

It's possible that the low may need adjustment but the high definitely doesn't. Link 3 has not sold for 20. I doubt anybody has in the last month. Downvoted until you show me conclusive proof that your range is good.

Counterproof:

http://www.tf2outpost.com/trade/9350320 -> http://www.tf2outpost.com/trade/9438129

Check the item histories of each hat. It was 1:1'd with a 16 key hat and had a 15 and 16 key pure offer.

The owner of the first link has done nothing for 7 months. It's very likely he would have taken one of the old offers. Notice that a poster even asked the trade owner to hide him, yet no action was taken.

http://www.tf2outpost.com/trade/9595095 - sold for 15 keys

http://www.tf2outpost.com/trade/8616234 - BO was 19 keys, unknown sold price

http://www.tf2outpost.com/trade/9435820 - sold for 18 keys + all father

http://www.tf2outpost.com/trade/9381277 - sold for blizz dread knot (17-20 keys)

http://www.tf2outpost.com/trade/9169455 - sold for about 21 in items

http://www.tf2outpost.com/trade/9050939 - this hat for n+b noir (13-16 keys)

http://www.tf2outpost.com/trade/8677710 - sold for 23 keys and some

http://www.tf2outpost.com/trade/9350320 - probably sold for bubbling nano (15-19): http://www.tf2outpost.com/item/440/1533229276/521/5

http://www.tf2outpost.com/trade/9303367 - BO at 18

http://www.tf2outpost.com/trade/9615985 - BO at 20

http://www.tf2outpost.com/trade/9637050 - BO at 20, 17 offered

Interesting, apparently people have sold this hat for a bit higher in the past... however, currently there are two BOs at 20, one at 18, and one at 17, all of which are unmet. 16 keys seems to have been offered pretty easily, so the low end of the price could use a slight adjustment. However, 20 keys is a bit high considering the unsold hats.