As I've said before here, in my opinion the presumption of coalition is not necessarily a good oner for a minor party.
Every coalition party in the MMP era has either been burnt by being too close to power (think Alliance), or is simply irrelevant (think Progressive). Which raises the question: How exactly should a minor party act when confronted by holding the balance of power?Seems to be that principled support such as this is better for everyone involved, and would certainly advance freedom while concentrating people's minds on what exactly "new coercion" looks like. There's plenty of it about at present.
If they're principled and in favour of more freedom and less government, then they have no problem: they can simply say "We will support every measure that advances freedom without introducing any new coercion." And then they would do so. Such support would be reliable (as long as freedom is advanced) and consistent. Such a policy is that followed by the Costa Rican libertarian party Movimiento Libertario, who hold 5 of Costa Rica's 57 Congressional seats, and it's worked fine for them.
I explain here how the studious application of this principle would suggest that killing the entire front bench of Government in their beds would be unprincipled; and here (scroll down to 'We'll get our fair share of abuse') how this principle would rule out support for a flat tax, for educational vouchers, and for state welfare being a 'hand-up and not a hand-out.'