Some of this is stage dependent and all of it is highly dependent on the team above the product manager. The simplest answer of course is to find PM's from companies who have had exemplary success where the Product Manager candidate either led prior success or was exposed to it in a meaningful way.
A simple starting point is to ask them to give you examples of conflicting opinions on a feature and how they evaluated the conflicting opinions and made a decision and tracked the success or failure of that decision.
AirBnb actually gives PM's homework as part of the interview process where they have to actually present a unique idea (from scratch) to the interviewing team.
Happy to talk to you about best process based on your stage and existing team.
I'm a firm believer in hiring a consultant to teach you what is required from a specific role within your organization. Instead of hiring untested talent or blindly interviewing people, come on here and find someone with a product manager background at a large successful company. Hire them to help you define the role for your company. Only then will you know what you need and how to lead them.
The best product managers can pick a product/feature they led and drill down to the various product angles and accurately articulate:
A. What was the process to define the requirements
B. What was the process to productize the requirements
By zooming in to the fine details and zooming out to the strategy and overall execution you should be able to evaluate a candidate.
When evaluate a PM I usually look for:
- Working in uncertainty
- Clarity of thought
- Data driven/informed vs. Guessing
- Be able to see the entire picture while zooming in to the fine details
- Technical Skills
The list above varies per company as in each industry and in each stage of a company the priorities are different.
Two great posts about product management:
How to hire a product manager by Ken Norton
Good Product Manager/Bad Product Manager by Ben Horowitz (appears with more details on his book "The hard thing about hard things")