If a candidate or their representatives publish false information in the election season and any citizen complains about it, the election commision can try the candidate and perhaps even ban the candidate from participating in the elections.
The onus is directly on the liar to not lie
So we'd have elections with no candidates at all. Or, more realistically, we'd have ones that have opinions matching opinions of those people who sit on the commission. Nice system, though it's not clear why bother with elections then at all - we just let the commission - after all, people who know all the truth must know how to select good people who tell the truth? - to choose suitable candidates. Elections where candidates that the commission doesn't like are excluded are no elections anyway - you can look at Russia how it works, they have "elections" exactly like that - people not approved by Kremlin largely just are excluded from participation, so nobody can vote for them.
Anyway, a good election commision can be formed by pooling career civil servants, equal representatives from each political party, a bench of retired judges elected by the Senate for a unit time.
The commision can not make any policy decision. All they can do is ensure that the elections happen in a clean way. Also banning is one of the extreme decisions, but if they do ban the candidate, the party has to provide someone else to contest.
A democracy where all candidates are liars is no better than Russian democracy where there are no candidates
In every democracy "all candidates are liars", if you call a liar anybody whose views can be contradicted by somebody else. Most of what candidates talk about aren't scientific facts, they are opinions and projections and moral judgements. Even about scientific facts there is considerable disagreement - what was considered a healthy diet a decade ago, is seen as a nutritional disaster now, so would a candidate that advocates old diet be called a liar? What about advocating current one - would such a candidate be a liar in a couple of years? Some economists think rent control and minimal wage are a disaster, others think they are a very reasonable and beneficial measures. If a politician agrees with some of them but not others - is she a liar? There's not a lot in what politicians say that can be scientifically and robustly verified as true or false - and those things that really can are largely inconsequential - even if some politician decides to proclaim pi equals 4, it's unlikely any actual policy would be influenced by that. So it would devolve into partisan bickering and gotcha hunting. Which you can amply witness on multitude of "factchecking" sites, which devolved very quickly from objective observers into presenting opinions as facts on one side into "factchecking" internet memes and obvious marked satire on the other.
That's a good thing. The views on governance policy can differ. I have no problem with those things.
I am talking about objective truths like Earth being flat, incorrect dates, misinformation in speech etc
There are grey areas here too, example being religion, and I concede that area becomes needlessly murky. Having said that, it needs to be discussed