Training AND practicing what the training covered. Hearing someone tell about something and how it works is OK, but without hands-on practice, it's gonna go away at the speed of light.

Do their reviews and have them concentrate on their weaknesses. Do they understand Ohm's Law and how it relates to what we do? I don't mean regurgitate it, I mean UNDERSTAND it. Can they wire a bunch of speakers without making an amplifier puke? Can they calculate a series/parallel load and can they come up with a ballpark estimate? Are they good at lacing racks? What about remote programming?

There's ALWAYS something that needs to be done.