Think about it via an analogy - do you know how to fix your own plumbing? If not, how do you know who to hire to repair your home? In short, you look at what they have done, listen to people who have worked with them, and react accordingly. Once you have hired someone, you have your own direct experience with them and can judge for yourself whether or not their work met your needs. If they meet your needs, then the relationship is working. If not, it isn't so you let them go and find someone else.

Technical people looking up from the bottom often expect some type of meritocracy where being good at your job earns you promotions and responsibility, but that isn't really how leadership works. When you are trusted, you get promotions. For exactly the reasons stated above - leaders delegate to people they have worked with before and trust that the needs will be met.

So as a leader, decide who you trust. As someone lower down the chain, work to build that trust.