I haven't seen anything in the Whitepaper about "Reputation" or "Trust" of users, but I think they would be required. This may require some form of registration process. Here are a couple of possibilities.

Regarding a peer-to-peer transaction, how do you ensure that both peers add the appropriate transaction fee to ensure it is confirmed by the network allowing both parties to receive their trade?

Example: User A exchanges Bitcoin for Dash with User B. Neither user sets a fee. User A receives Dash right away, User B sees the Bitcoin transaction broadcasts to the network but it never gets confirmed.

Could it be possible for a user to outperform the validator's verification and transaction broadcast process causing a double-spend transaction and resulting in one user ending up with nothing?

Would a "Report User" feature be required if someone gets screwed out of their transaction?