I'm still a licensed landscape architect in California, even though I don't practice there anymore (who knows, I may give some advice on my next visit). We architects and contractors in California are very familiar with the California State Board that licenses contractors, receives complaints about contractors, and checks out the complaints and requires, or doesn't require, remedies or rescinds licenses.
Licensing in California is a serious concern. If you hire a licensed person you will have recourse if you have future complaints. Not that all licensed people are terrific, nor that all unlicensed are dismal, but there is a competence test to past re practice and professionalism to get that license. I consider that test minimal.
Well, here's a starter link - http://www.cslb.ca.gov/
Hah, I say that, but have to research the exact link for you. Back in a minute.