Vaughan Smith, a friend who put Assange up at his country mansion for more than a year, addressed Westminster Magistrates' Court last week on behalf of the nine, who put up £140,000 between them.
He said all those who offered sureties, of varying amounts, are "convinced that they have done and are doing the right thing".
In his ruling, the Chief Magistrate said he accepted that the nine had all acted in good faith, saying: "I accept that they trusted Mr Assange to surrender himself as required. I accept that they followed the proceedings and made necessary arrangements to remain in contact with him.
"However, they failed in their basic duty, to ensure his surrender. They must have understood the risk and the concerns of the courts.
"Both this court and the High Court assessed that there were substantial grounds to believe the defendant would abscond, and that the risk could only be met by stringent conditions including the sureties," he said.