Hey, can someone plz awnser some stupid questions from a Newb ?

1: Is there possible to dupe items in closed b.net now (1.09) ?
2: If yes, How ?
3: is there anyway to protect myselfe from trade hax or such things ?
4: is there any way to know if an item is dupe ??


Thx 4 any awnser..
**Btw this is my first thread & post =D**