Re: Financial Decisions
That's easy - the person who's better at managing the finances.
When I was growing up, it was always my mum who had the final say. My parents have always discussed every financial decision together and generally arrive at something that suits both of them, but when they can't, my dad usually lets my mum take the lead. Not because of any sentimental reason, but simply because she's better at handling money. He overspends; she can strike a balance between investing and spending. So it's kind of logical that she makes the final decision.
Me and my guy, we mutually decide what we need, prioritize things we need to purchase, and then we pool in what we earn. There's no clear-cut 50-50 deal, but that's kinda of how it naturally works out. So if we need, say, a microwave, I'll purchase it and if next month we need a dishwasher, he'll get it. But deciding what to send money on - no matter if it's his or mine - is always a mutual decision, unless it's a gift or a surprise or something like that.
For decisions like which place to purchase from, if/ where to invest, I let him take the lead in things he's better at it, and he lets me take the lead in things I'm better at. So if we're renovating, he'll let me handle the finances because I know where we can get the best deals. If it's a mutual fund, I'll let him make a decision because he's actually practicing finance, so he knows a lot more. So even with us, it's kind of what I grew up watching my parents do - talk things over to get a wider picture/ more perspective (a lot of the times, we haven't thought about certain aspects that a partner can point out) but, once you do have the full picture in front of you, whoever's better at making a certain kind of financial decision should be the one to make it.
As for disagreements - they always happen, but we don't get riled up or angry over it. We have a rule: no shouting or raising voices, no matter how frustrated we get. ;p I explain my side of the picture to him, and he explains his to me. What I've seen is, most people go into an argument with the aim of convincing the other person that they're right. We try to do things differently, by actually considering what the other is saying. Generally, we're able to find a middle ground.