It is the City or County that usually handles licencing for Tradesmen and Contractors. There should be a Code office near you that could give you the information or a number to call. You can also check the local BBB but they are not always a big help. Some areas also have Contractor Associations that can be contacted. As far as past jobs, it would be best to ask him for references. Most contractors I know have an album of past job pics and a list of satisfied customers you can call.
If you have never made a mistake, you haven't done much.