When hiring a person who has been certified you know that that person or persons has been trained properly and well and they know the critical intricate part of cleaning your home or office. 
Hiring a professional cleaning service for your home or office is because they are the ones who can resolve the problems with your home or office. 
Professionals know the chemical make up and what is environmentally friendly and human friendly as well to ensure client safety. 
Professionals know the proper ways or cleaning absolutely every part of your house or office. 

Professionals are able to get rid of any major problems and you feel safe because you can and are able to trust them because you get to know them and with their professional knowledge of the type of cleaning your receiving.