Great question...

A pesticide applicator's certificate (commercial or private) is needed to purchase restricted use pesticides. None of the pesticides available at common retail outlets/hardware stores fall into this category.

Any time pesticides are applied 'for hire' (i.e., as part of you employment), the State of Michigan requires that the applicator has a current Commercial Pesticide Applicator's Certificate either from Michigan (MDARD) or a state in which reciprocity is recognized. 

Private certificates are required for individuals who will apply restricted use pesticides to their property or the property of their employer. These are typically used by agricultural producers for their own property.  

You can find the answers to more questions and look up applicator credentials at the following website:
https://www.michigan.gov/mdard/licensing/pesticide/pesticide-applicator-certification

If you have any other questions, please let me know.