Here are a few ways for you not to get scammed while trading or lose all your items/account.
1. Avoid trading with suspicious characters. Example, There is someone , without any set or wings that you never seen in game or any other peope from you alliance/guild know anything about, selling some stuff that a new character can't easily get then again use common sense and avoid trading with that person.
2. Move to a different location to 'trade'. Theres no reason to move to some location like arena for example if the person is selling his/her stuff in lorencia. That doesn't sound right is it? Something might be wrong here.
3. Never trust someone telling you for example, 'give me your items i know a way to dupe them'. Instead take a screenshot and post it here so we can handle that person.
4. Never 'lend' stuff to strangers. Example, someone says he wants to try the items before buying. Theres no need to do so.
5. Want to sell something for items instead of zen? Make sure you are maxed on zen (2,000,000,000) so they can't buy from your shop for zen.
6. If you play on a cafe make sure when you leave the place you are siting you log out so others can't play or steal stuff from your account while you are away.
7. When you play on a cafe make sure you change your password as soon as you get somewhere you trust. Cafe might have keyloggers, better safe than sorry.
8. Take screenshots when you trade. This will help you have proof if you need it later.
9. NEVER tell your password to ANYONE. Even GM will NEVER ask your password. If someone comes and tell you for example 'hey im an GM and i need to look your account give me your username and password', take a screenshot and post it on the forums so we can handle that person. Also if you tell your password to friends and something is missing remember we most probably won't return the items if we see more than one person logged on your account.