Please explain what happened in detail.
ScrapTF | Scrapprehensive send to me trade offer. 12 keys and 13.77 ref on scrap.tf. I accepted trade offen. Scrapprehensive get Nuts n' Bolts Salty Dog, but i don't get 12 keys and 13.77 ref.
Did you have any conversation with someone about this trade before you made it? or did you just go to scrap.tf to sell your hat?
I go to scrap.tf to sell.
So it is likely your Steam Account got Hijacked, and the hijacker redirected the trade to steal your items
Basically, the Hijacker cancelled the trade with scrap.tf, then sent another trade that looks exactly the same
If this did happen, there should still be proof the trade scrap.tf sent got cancelled
On your steam account, look at your incoming trade history and see if there is a cancelled trade from scrap.tf
This can be found here:
https://steamcommunity.com/id/Your Steam ID/tradeoffers/?history=1
(Replace where it says 'Your Steam ID' with your Steam ID)
I have cancelled trade offer ScrapTF | Scrapprehensive and accepted from scammer. https://steamcommunity.com/profiles/76561198870388474
If you randomly decided to sell the item on scrap.tf this wouldn't have happened. You surely must have had a conversation with someone where they asked you to sell on scrap.tf or they asked you to check the items price on some random website, on which you logged in and they got access to your account and swapped the trade.
Try to remember. If you did speak to someone we would need the chat logs for that. If you did not then there is nothing much we can do here. I have banned that account from the site.
Closing due to lack of follow up. You can reopen this yourself if you would like to add the required evidence.
A guide on reporting can be found here - https://forums.backpack.tf/topic/53663-guide-for-reporting-on-the-main-site/