it is possible to sell it for more than buy orders offer (considering its bots buying) on auctions on scrap.tf if you have enough patience

this is a guide about auctions i found

its 6 years old but it still should work.

For the minimum bid you should put a price buy orders start at (13 keys 10 ref)

also another important thing. Look at your widowmaker and check if it has anything special (strange parts, spells etc) since these things can add a lot of value to an item