https://backpack.tf/profiles/76561198328624791#!/compare/1526428800/1526515200

https://backpack.tf/profiles/76561198341086501#!/compare/1526428800/1526515200

Bulk.

https://gyazo.com/0f2e4ee9f9b31bac34dc7662f1b6161d

https://backpack.tf/profiles/76561198309332284#!/compare/1530835200/1530921600

Apparently sold for 8.5 keys? Compare links do not reveal anything. Supports including 8.5 I guess.

https://gyazo.com/eccef753aa84a43f915d80cda236d77e

https://backpack.tf/profiles/76561198309332284#!/compare/1525219200/1525305600

https://backpack.tf/item/6595151621

The marketplace.tf sale here on the 11th of May at $18 was sold by the same bot (withdrew, then deposited to marketplace) that had a B/O of 8.5 keys on when he had this hat earlier, meaning he likely had a 8.5 key B/O back then as well.

So based on the fact that the B/O for the $18 sale was high likely 8.5 keys and that there's also likely a 8.5 key pure sale I would go with 8.5 keys here. The first sale took atleast 2 months at 8.5 keys and the other possible pure sale at 8.5 keys took 1.5 months as well ( https://backpack.tf/item/6595151621 ). Based on that, I'd exclude 10 keys. Seems rather high and a lucky sale. Not to mention it's a marketplace sale which are often high on low tiers.