Well so far I have had no luck finding his license either but I will keep looking.
Now I did see this from the:
State of Michigan
Department of Labor and Economic Growth
Division of Commercial Services
Enforcement Division
The department, as a matter of policy, does not investigate complaints against a person or business who practices an occupation or profession without obtaining the required license. This is a criminal offense and is the primary responsibility of the local prosecuting authority. However, the Enforcement Division will assist the prosecuting agency as
This is also from the State's website:
Michigan State Board of Residential Builders and Maintenance & Alteration Contractors
The Michigan Residential Builders and Maintenance & Alteration Contractors Board was created under Article 24 of Public Act 299 of 1980, as amended, to license and regulate persons engaged in the construction of a residential structure or combination residential and commercial structure, or persons who undertake the repair, alteration, addition, subtraction or improvement of a residential structure or combination residential and commercial structure for compensation other than wages for personal labor.
A state license must be displayed in the place of business and all contractors and their salespersons must carry a pocket card which you should ask to see. If they cannot show you a license, check the department's License Information database or call the Verification Unit at (517) 241-9288.
Now I am not positive about this. The highlighted portion above concerns me as to this being the appropriate authority. With it being a company though, I would believe it is the correct department to talk with. Try the phone number. They may be able to help you find this guys license. As posted above though, if he did not have the required license, it is a criminal offense. Your local prosecuting attorney/district attorney office would be the place to contact to report this guy.
If he doesn't have a license, I think it makes it easier to win a judgement for your money since he isn't supposed to be doing this at all.
If he has a license, there is a complaint section around the link I posted before. If all else fails,"www.mi.gov" will get you to the beginning.
Ultimately you may need to sue this guy. Some research into the license situation may be prudent before showing up in court. The courts will probably accept a sworn statement from other contractors as to the quality of work but they would rather be able to question the person themselves. A statement will not carry as much weight as a witness.
Maybe he will see it your way if presented with the other possibilities.