"I've been appalled by the refereeing, especially how they have decided games with scrum penalties," Mains said.
Mains said that it had gotten to a state where guesswork could influence decisions.
"Games have been won and lost from scrum penalties when the wrong decision was made. You should not have a situation in rugby where games are won and lost by the referee's guess," he said.
Mains said the thing that concerned him most were the grey area that the scrum had become, the inconsistency in the rulings and unnecessary penalties.
"A lot of times when penalties were awarded, I couldn't tell who was at fault. There was no way that the referee knew. It should have been a reset scrum."
Mains, the last coach to take New Zealand to a World Cup final in 1995, was confident, though that New Zealand would beat France in the final, and gave Jerome Kaino his vote of confidence for player of the tournament.
Mains took a pot-shot at fellow New Zealander Bryce Lawrence when he admitted that he would have preferred a final with Wales or South Africa, teams he thought were taken out of the tournament by bad refereeing decisions.
"I would have felt a lot better about winning the World Cup if Wales or South Africa had been the other team in the final," Mains said.
"They would have been worthy opponents for the All Blacks."