When interviewing a developer they may sometimes provide samples of their previous work for review (where an NDA does not prohibit this.)

This can be effective however it's difficult to know if they really worked on it and, if so, how much they did and how much was done by others on the team.

This is why I value a developer's open source contributions more than past projects.

It's virtually impossible to fake open source contributions.

Working on open source projects can be difficult and frustrating, especially because there's no pay involved. This shows strength of resolve.

Similarly, open source projects are notorious for having a high barrier to entry and can be quite a challenge to one's ego. This shows strength of character.

Next time you're hiring a developer ask to see their GitHub profile.

While you may not fully understand what you're seeing, a regular history of accepted pull requests is a good indicator to look for.