I've found a new scamming method, not sure if anyone else has encountered it.

The victim starts an auction on scrap.tf. The scammer, who doesn't have mobile auth, bids on the auction, and wins in. In the comments, they discover that they cannot finish their bid, and so offer to send the item outside scrap.tf and eat the 7 day trade ban. The victim agrees, and the scammer sends the item in a trade, triggering the 15 day trade hold. After a few days, the scrap.tf auction is cancelled, the scammer is trade-banned and the victim receives their item they were auctioning. The victim then sends their item, and uses mobile auth to confirm it. The scammer receives the item, and immediately cancels their trade, ending up with both the auctioned item and the bid.

Happened upon this while I was checking my auctions on scrap.tf. I won a bid on a Strange candy cane, but couldn't finish it because I haven't had mobile auth active for 7 days. Sent the bid items directly to the auctioneer as an act of good faith, before realising how this could potentially turn into a scam.