I've led teams, hired people, worked with externals. After all those years, there are only two qualities I look for.

First: are they willing to iterate.

Working with externals taught me a quick test for this. Watch how they react to your first round of feedback. If they iterate with you, good. If they defend their first version like it's their kid, that's the red flag. You're not buying art. You're paying for a service, and your direction has weight in that room, because you're the one paying and you're the one with the vision.

The same applies inside the team. If you hire a programmer who wants to dictate how the code is written while producing 5% of it month to month, let him go. The only thing he brings to the team is distraction.

Second: do they work on themselves outside of work.

Are they learning on weekends, reading, building side things? That's how their value actually grows. And the funny thing is, you don't even have to ask. If they do it, you can just spot it.

But there's a part nobody talks about. People who invest in themselves expect more in return. They'll come back and ask for a raise. And they'll usually be right, because their value really did go up. Refuse to pay it and you get the publishing house story I wrote about: one good person gone, five mediocre ones hired to replace her.

So hire people who iterate, and hire people who grow.

Just be ready to grow with them.