Before customers even, business founders can offer the credible promise of customers. The credibility comes from some sort of market validation. They should be able to convince you that a good execution will actually get traction, and help discover discover early that product X is not what people need/will pay for, but close variant Y is what should be focused on instead.
In my very limited experience, non-technical partners have vaguely done this, but haven't clearly communicated what they're doing or how it contributes value. I think they imagine that I share their background, and automatically understand and value their actions. With no shared background, poor communication, and only a short relationship with them so far, the trust isn't there to really value their work.
My mistake has been looking forward too much to what a product will be, and thus aiming for more than is reasonable in a small, fixed timespan. This inevitably means I can't achieve what I aim for without investing significantly more of my time than the non-technical partner, which makes me feel like I'm getting a bad deal. I have to learn to aim more minimally, and estimate more generously.
It seems that both types of founders need to communicate a lot, and invest more in the personal relationships outside the venture. All that communication will build the trust which eventually makes things flow well and happen efficiently.