+ Reputaion is for everyone who gets "+reps" for being a friendly person, active community member, fair item trader and/or an honest gamer.
Pointers when dealing through a steam trade:
1) If people are writing in very bad english, don't trust them.
2) If they are called [unassigned], don't trust them.
3) If they haven't yet setup their profile, don't trust them.
4) If they are in a hurry to trade, don't trust them.
5) If they send you a link to their offer, don't trust them, and DON'T click on their link.
6) Pay close attention to people with Private Profile or an empty Inventory.