If you have for example, enchanting and can make for example mongoose.
You can trade someone say, that you have all mats and will enchant for exmaple 700gold, open trade with the victim and put mongoose on hes weapon but don't accept until he had put up 700gold and accepted, when you press accept you walk forward exactly same time. That way the enchant won't come on the weapon, and you will keep the mats and the gold you got by the victim.