Thank you for the link , it's pretty useful .
However I can't seem to understand what those Arbitration companies do exactly ? and what if after the Arbitration the user Deny or refuse to re-pay what would happen ? Also all countries have those Arbitration stuff ?

Btcjam doesn't really protect you. The netarb (best case scenario) will just allow you to receive personal information of the borrower - such as home address and full name and phone number. I got scammed on btcjam a year and a half ago and the net arb didn't do shit :-/