Instead of promising to “balance the budget”, have them produce a budget plan

Many parties do produce a vague budget going into the election, but it still doesn't account for unexpected events like the pandemic. And even though "balance the budget for 4 years" is a somewhat reasonable promise, creating a budget 4 years in advance is a terrible idea for so many reasons. Even just through the normal course of an uneventful term, things will change that the government has no control over, and if they can't react by modifying their budget that they made several years ago, then that will cause a lot of problems.

And if their promise is something vague like "balance the budget" and there are legal consequences to not balancing the budget, then the government would be encouraged to sell of infrastructure in order to make up any deficit they may have accrued. That's also bad.