One of the drawbacks to shared stashes is that characters have infinite access to all their torches. so even if they link one, they can be holding another. Also show the torch in trade screen before you do the drop trade. If they go back to the their stash definitely dont drop your torch to trade. They can link an item from their stash, not hit enter on the chat log, move away from the stash, hit enter to "show" the torch you want. You link yours. Trade torches and find yourself the owner of 10/12 amazon torch.

Also keep a running list of the name and bnet id of people who try and scam you. Once a scammer always a scammer - avoid trading with those players.