I usually have a strict code whenever I'm trading. It's to double check the item before i accept it to make sure it's not a counterfeit. One thing i make sure is how they're willing to overpay for an item.
Plus I don't really interact with anyone that much in the game, so it's quite easy for me to extinguish the behavior of the players :p. Just make sure you're not dealing with anyone that has a history of anything illegal,