As the polls were closing at the recent North Shore byelection, TV journalists were relaying senior ministers' pessimism about the government's campaign, one botched by a candidate accused of fibbing.

"Even the Premier is furious," said well-connected Channel 9 correspondent Chris O'Keefe.

About two hours later Gladys Berejiklian was jubilant. She emerged raising her hands, as you do, and thanking voters for trusting a candidate colleagues had been preparing to push forcefully into moving traffic two hours ago.

"The strategy worked, just like we thought," said a senior campaigner.

Just how it did, though, raises some questions about the way elections in NSW are running.

The Liberal campaign rested on a pitch to discourage people voting for anyone other than the Liberals from marking preferences.

On election day and at pre-poll stations voters were handed flyers in black-and-white, not Liberal blue, that read: "You can just vote 1 on the assembly ballot paper".

On the small print these were authorised by one Chris Stone, who was not identified beyond his address.

People who are not members of a political party might not know that Stone is the director of the NSW Liberals.

The virtues of leaving it up to voters to choose whether to mark preferences are well rehearsed: it's more democratic to not express a choice if you don't want to, advocates say.

That's probably true. But how well informed were the voters about this, especially in the face of a misleading campaign?

North Shore Greens voters, I tend to find, are all the stauncher for being surrounded. Most would prefer being eaten alive by wild horses to Liberal government.

But roughly one-third of their ballots did not travel on with preferences, suggesting they were indifferent about whether they were represented by a Liberal MP or the leading alternative, an independent.

I wonder how many of those about 2200 Greens voters (and many more independents) might think about their votes again, following a final post-preferences result that had the Liberals lose by less than 3500.

Some protested they believed "just voting one" would have preferences automatically distributed, as used to happen in the old Senate elections.

What is clear is that not marking preferences likely made the difference.

If trends held and the North Shore election were run using the same system as federal elections, which requires voters to number every square on their ballots, a different woman would likely be entering Parliament.

This election had by no means an unusually low "exhaustion" rate of preferences for NSW Greens voters and second-guessing voters' intentions can be a very divisive game.

But it's fair to ask whether these voters knew the implications of their choices.

Come September, some North Sydney residents will be perhaps the most electorally exhausted in Australia, having voted in six polls in 2?? years across council, state and federal elections.

Each time they will negotiate a system that treats marking and allocating preferences differently.

Queensland recently ditched optional preferential voting after the Liberal government was bested by a union push to have voters number every box making use of similarly misleading, official-looking posters. NSW is now the only state to use a fully optional preferential voting system.

There is evidence at least some voters are confused.

At the last federal Senate election the rate at which NSW voters either cast informal ballots, or did not have preferences allocated, was up to 50 per cent higher than the national average.

The results in North Sydney will now be challenged in court by losing candidate Carolyn Corrigan. Her complaint says even electoral commission officials told some voters to "just vote one", something the commission denies.

It is clear, however, that public information campaigns for the byelection were inadequate. In its official pre-election information brochure the commission does not explain how optional preferencing works in NSW.

The ballot does mention voters can number more than one box, but it does not offer a complete explanation of how preferences work.

Debates about the electoral system are tedious and a hundred years old. Conservatives long favoured compulsory preferencing but now Labor does as the progressive vote splinters between it and the Greens.

That is much less important than ensuring voters know fully the implications of their vote and how to navigate different levels of government.

The party of government in NSW misleading voters with perfectly legal material is an ugly thing indeed.

But it's a tactic that can only work when elections happen in a vacuum of voter knowledge and regulation.