According to this Trickster's Turnout Gear stats page on TF2Stats:

[url]http://tf2stats.net/item/Trickster-s-Turnout-Gear/30169/[/url]

only 0.1% of players have a Strange Trickster's Turnout Gear found in their backpack.

This can most likely be attributed to the item's distribution through the Unlocked Pyro Crate found in the Mann Co. Store, which, according to my knowledge, is the only place where a Strange version of this cosmetic can be acquired from.

I recently acquired my own Strange Trickster's Turnout Gear from the Steam Marketplace at $19.00, which was the cheapest value on its Marketplace page. At the time of purchasing, there were only 2 up for sale, the other one priced at $34.50.

[url]http://steamcommunity.com/market/listings/440/Strange%20Trickster%27s%20Turnout%20Gear[/url]

Now, the reason for the 9 key price suggestion is not based upon its current Market price, but rather on the price of a similar Strange Pyro item, the Last Breath, which also currently goes for 9 keys. In addition, the Last Breath also has a similar Unique-to-Strange ratio as the Trickster's Turnout Gear on its TF2Stats page, suggesting a similar rarity.

[url]http://tf2stats.net/item/Last-Breath/570/[/url]

I hope you take these points into consideration when choosing this item's price, and I thank you for reading.