This can be separate tip, although it’s been mentioned above. Chances that person who’s trying to scam you, scammed someone before. So, besides asking mods, admins or other members, you can perform your own background check. You can search for suspicious trader username and email or Instant Messaging address in the major search browsers like Google. Results you got using this method, can be useful to reveal if you are dealing with a scammer.
You can even include ‘scam’ besides name and email to boost the search and get the right results.