You want to work with people who share your values.
Of course you want to work with people who have integrity but even if they have it and you don't value the same things then there's a mismatch of incentives.
You particularly need values-fit early on in a startup's life.
How do you test for values? It's really hard. Time certainly helps but that doesn't always work especially when you're trying to move fast.
A good way to test for values is to simply ask them what they value and why. Why do they want to work on this project? What motivates them? Why are they motivated by that? Get to the core of their humanity by getting to know them.
Probe early and often. Ask direct questions to get honest answers. Trust your gut.