The "Complete" Job?
The most important question is are you getting a complete kitchen exhaust system cleaning of your entire system? Often managers think they are getting their entire system cleaned only to find out what they have been receiving is merely a "hood shine". Additionally, checking the work is difficult, most systems were not designed for maintenance and some managers may not know where their exhaust system goes. Knowing the type and exact location of your grease exhaust system, including fan and duct work, will help you recognize how they are going to clean it.
You should alway receive a written proposal outlining what the commercial hood cleaning company is going to clean and how they are going to clean.