In discussions at work about hiring developers, certifications were never considered to be valuable. The general view was that while a certification might mean a candidate was 'book smart', whether they could apply those skills well and build good systems was in question.

Bringing code samples was considered very helpful, as was clear descriptions of systems built with specific technologies. Those descriptions were also very useful in determining breadth of skills with specific languages. Some times a manager wants someone with specific skills to fit a certain role. Other times, they want someone that is more versatile and doesn't mind switching jobs between projects.