I've done several approaches:
- homework project
- heavy interviewing with plenty of tests and several (3-6 people) giving written feedback on the candidate in the form of 5 points rating on lots of skills
- hire on gut feeling
mixed in various amounts.
In my case, a diploma/certificate doesn't make me feel better. I've seen plenty of incompetents with a diploma, so I don't take it at face value. Testing worked best for me.
A diploma/certificate also doesn't tell you anything about the candidate's work style/attitude. A hire with a bad attitude is much more toxic than a hire that lacks technical skills.