c-darwin

It will be difficult to get a dishonest reputation, because statistics gives the information on miners (http://en.dcoinwiki.com/Miner). A buyer and a seller should trust the same arbitrators. Which means that each and every arbitrator should earn not only buyers' trust but sellers' too. Eventually, I think, there will be a few respectful artbitrators, and most of buyers and majority of sellers will trust them.

No, you have quoted the description of arbitration (http://en.dcoinwiki.com/Arbitration) which is just an additional option, it is not a must to use it

Access to the account is only possible using the private key. There is also the private key recovery function: http://en.dcoinwiki.com/Restoration_access. However, there is a problem with twins. Only one of the twins will be able to become a miner, another will have to use a regular anonymous account.