s. 142 (Admissibility of evidence: standard of proof) of the Evidence Act 2005 (NSW) notes that evidence will be usually admitted if the Court is satisfied that the facts have been proved on the balance of probabilities. The matters that the court must take into account include (summarised – see legislation for full version): (a) the importance of the evidence in the proceeding, and (b) the gravity of the matters alleged in relation to the question.
David Hamer, in his very interesting and informative article ‘Chance Would Be a Fine Thing: Proof of Causation and Quantum in an Unpredictable World’, for the Melbourne University Law Review in 1999, noted that
It is well established that, while the civil standard is the balance of probabilities, the precise meaning of this expression depends upon the circumstances of the case and, in particular, what is at stake for each of the parties. … Where the plaintiff’s allegations have moral overtones, as in fraud or adultery cases, the civil standard may be higher than where mere negligence or breach of contract is alleged.