Cleanliness of restaurant kitchen exhaust systems is the restaurant owners responsibility.
Whether of not your restaurant hood system is maintained properly is ultimately the responsibility of the restaurant owner.
Here is an excerpt from the California Mechanical Code:
CMC 507.1 Exhaust System – The responsibility for inspection, testing, maintenance, and cleanliness of the ventilation control and fire protection of the commercial cooking operations shall ultimately be that of the owner of the system, provided that this responsibility has not been transferred in written form to a management company, tenant, or other party. [NFPA 96:4.1.5]
What this ultimately means is that if you do have a hood cleaning company service your restaurant exhaust system, and they are not doing it properly, the responsibility lies on you, the restaurant owner.
Here is an example of a system that had been getting serviced regularly but key hidden areas of the system were being missed resulting in approximately 100 pounds of grease build up
Many kitchen exhaust cleaning companies will offer free inspections with pictures so you can see how well your current company is cleaning your exhaust system. If you haven’t seen pictures of your kitchen exhaust in a while, it would be a good idea to have it checked.