-Sold with a sulph big chief + ~4 keys in sweets (though this does seem very high): http://backpack.tf/profiles/76561198116082946#!/compare/1487548800/1487894400

-Sold with 7 keys for a vivid noir: http://backpack.tf/profiles/76561198130990555#!/compare/1488153600/1488240000

There are probably more sales in this very history, I can help you look through it later if you'd like but 18 might not be right: http://backpack.tf/item/4954568502

https://marketplace.tf/items/30406;5;u16

Sold for $42 ( / $2,10 ) = 20 keys

http://backpack.tf/profiles/76561198061402527#!/compare/1490659200/1490832000

?

http://backpack.tf/profiles/76561198294607730#!/compare/1490140800/1490227200

Bulk.

http://backpack.tf/profiles/76561198116082946#!/compare/1487548800/1487894400

http://www.tf2outpost.com/trade/28797515 - reselling with 22 key b/o

Taking from Fish above, he sold it for the Sulphurous Big Chief + 4 keys in sweets. He was reselling it with a 22 key b/o means that he didn't value it at 28+ himself either.

http://backpack.tf/profiles/76561198130990555#!/compare/1488153600/1488240000

Mini for the Noir:

https://marketplace.tf/items/319;5;u16

Sold for $47,50 ( / $2,10 ) = 22,6 keys = 23 keys.

http://backpack.tf/profiles/76561198047609644#!/compare/1493683200/1493942400

22 keys (noir)

18 flat is definitely not going to correct. I'd go with 17-22 based on the sales, although the Noir might need a bit more digging. You can make a suggestion on that as well if you'd like.

Closing on account of sufficient counter-evidence. Feel free to fix.